Spell and Trap Cards provide even more color to the game, making the battle between the same beatsticks over and over much more intereasting. We all know how the mighty Mirror Force takes care of every opposing monster that even dares to declare an attack, or how Brain Control turns around almost any situation (and defines most games, but that's a different story >_>). Most people are really familiar with the various types of S/T Cards, but not with most of their mechanics.
Before we start, there's something that needs to be said and everyone should burn in their minds: S/T Cards are NOT sent to the Graveyard immediatly when you activate them. Keep them on the Field until the chain is done resolving! If you want to activate Mirror Force, flip it over. Do not swing it on the air and make it land at the Graveyard, that's not how you activate a Trap Card. Specially for Normal Spell Cards, which are always "dumped" from the Hand to the Graveyard. This is when the various electric shock devices from the anime would come in handy...
Okay, let's ignore crazy fetishes and move on. Normal Spell Cards and Normal Trap Cards are quite evident, so they don't need too much explanation. We'll return to them in a minute, though, so keep them in your Hand. Let's take the chance to clarify that "Magic" Cards are treated as Spell Cards. Should be obvious, though.
We then have Ritual Spell Cards, identified by a pyre symbol. These work exactly like a Normal Spell Card ruling-wise, so once again, not much explanation is needed.
Moving on, we have Continuous Spell and Trap Cards. These are identified by an "infinite" symbol (or Leminscate). Finally, we have some mechanics to explain. Continuous S/T Cards often have Continuous Effects. Before you die of redundantitis, the point here is that these Continuous Effects will not be applied until the Continuous S/T Card resolves. So, for example, if you activate Royal Decree, the opponent can chain Dust Tornado to destroy it, as Decree's Continuous Effect has not started applying yet. This is different from a monster's Continuous Effect, which is applied immediatly as soon as the monster is face-up (for example, you can't use Trap Hole on Jinzo).
Continuous S/T Cards may also have Trigger-like Effects, Quick-like Effects, or Ignition-like Effects. These names are borrowed from Monster Effects to explain how they work. So, for example, an Ignition-like Effect is one that you activate manually during your Main Phase, often by paying a cost (such as Core Transport Unit or Blaze Accelerator), a Trigger-like effect is activated when a certain trigger is met (such as Robbin' Goblin or Ectoplasmer), and a Quick Effect is often chained to negate effects or activations (such as Royal Oppression or By Order of the Emperor). All of these effects use the chain, as their counterparts in Monster Effects, but also, since we are dealing with Continuous S/T Cards, if the S/T Card is not face-up when this effect resolves, then it will resolve without effect. For example, if you activate the Quick-like effect of Royal Oppression, and your opponent chains Dust Tornado, Oppression's effect will resolve without effect. This is also the opposite of Monster Effects, who will resolve properly most of the time if the monster is no longer face-up. Of course, this doesn't apply to Continuous S/T Cards that are Removed from the Field as their own cost (such as Wave-Motion Cannon). Now that would be redundantitis.
Equip Cards are identified by a cross symbol, and they follow the same rules as Continuous ones, with a few more of their own. A quick tip about them is that Equip Cards always target, and in general, you can equip them to any face-up monster, not just your own. If its target disappears, they are destroyed by Game Mechanics. If an Equip Card is activated, and an effect is chained that Removes it from the Field, it will not be treated as being equipped to a monster. For example, if I activate Butterfly Dagger - Elma, and my opponent chains Mystical Space Typhoon, Elma's effect will not activate, as it wasn't "equipped" to a monster.
Certain Cards that are not Spell Cards can become Equip Cards too. Monsters become Equip Spell Cards, such as Union Monsters or monsters targetted by Destiny Hero - Plasma, and Trap Cards become Equip Cards, but remain being treated as a Trap Card. In other words, an "Equip Trap Card". This happens because monsters cannot exist in the S/T Zone as Monster Cards, so they are treated as a different type of Card. But since Trap Cards can exist there, they remain treated as Trap Cards (such as Blast with Chain). Of course, every rule applies. Some may mention Crystal Beasts, too, which become Continuous Spell Cards, but they merely sit there doing nothing, so they aren't important ruling-wise.
Field Spell Cards are identified by...some sort of upside-view-of-a-mountain-symbol. They also follow the same rules as Continuous Cards, and also have a few of their own. The main thing you should check with Field Spell Cards is who they affect, as they often affect both players, but more recently, they started having one-sided effects, such as the cost-substitution effect of Brain Research Lab.
There can only be 1 active Field Card at the time. This means that both players can control a set Field Card, or one player can have an active Field Card while the other one has a set Field Card. Unlike any other type of Card, you can destroy your own Field Card in order to have a new Field Card take its place. This destruction happens by Game Mechanics, and it happens immediatly before the new Field Card is activated. However, this is different if there is an active Field Card, and the opponent wishes to activate a new one. In that case, both Field Cards exist on the Field at the same time briefly, until the new Field Card resolves. When it does, the old one is destroyed by Game Mechanics. If the new Field Card is Removed from the Field before it resolves, the previous one remains intact. For example, if I control Future Visions, and my opponent activates Geartown, I can chain Dust Tornado to Geartown, and Future Visions will remain on the Field.
The last type of Spell Card are Quick-Play Spell Cards, identified by a lightning-symbol. These are the only Spell Speed 2 Spell Cards. In most aspects, they work as Normal Spell Cards, only that you are allowed to activate them from your Hand outside of your Main Phase within your turn, and during the opponent's turn as well if you choose to set it. Their only "hidden" ruling is that, if you do set them, you cannot activate them during that turn. This is the common rule for Trap Cards, but this does not apply to any other Spell Card.
Finally, we have Counter Trap Cards, identified by a returning-arrow-symbol. The only Spell Speed 3 effect in the game. They work much like Normal Trap Cards, only that their high speed makes them much harder to retaliate. A relevant ruling is that most Counter Trap Cards do not target.
This covers most aspects of Spells and Trap Cards. There are a couple more things to mention, though. The first is the key difference between "negate" and "destroy". Remember that I told you to keep Normal S/T Cards in mind? This is where they get useful. Normal S/T Cards, and those that work much like them (Ritual, Quick-Play, and Counter ones) will NOT have any issues if you chain to them with an effect that destroys them. For example, chaining Dust Tornado to Raigeki will NOT prevent the destruction of your monsters. You need to negate these Cards in order to prevent them, such as with Magic Jammer or Dark Bribe. Chaining a destructive effect only disrupt S/T Cards that need to remain on the Field, namely Continuous, Equip, and Field ones.
The last thing to address is returning activated Cards. You cannot return an activated Card to the Hand or to the top of the Deck if that Card will not remain on the Field after its activation. For example, you cannot target Heavy Storm with Phoenix Wing Wind Blast, as it is known that Heavy Storm will not remain on the Field after the chain resolves. One could say it is "marked for destruction", although deeper information is still somewhat obscure. A much more relevant example would be that if you target a face-down Jar of Greed with Raiza the Storm Monarch, and Jar of Greed is chained, Jar will not return to the top of the Deck. An even more evident is example is how Giant Trunade does not return itself to the Hand. This only applies to Normal, Ritual, Quick-Play and Counter Trap Cards, as the others do remain on the Field after their activation. It also applies to the rare cases in which those 4 types of S/T remain on the Field thanks to their text, such as Swords of Revealing Light or Blast With Chain.
That sums it up for S/T Cards. If you have any questions, feel free to drop me an e-mail at ness00[at]gmail[dot]com.