How to play a Shadow Priest in WoW, basics.

--So you want to be a shadow priest, eh?

     The Priest class in World of Warcraft is not just for healing. Shadow, the third specialization choice for priest, is an all out damage dealer that does damage with DOT spells. This hub will provide a very basic guide for how to play your Shadow Priest.

--Leveling as shadow priest.

      First of all, I would recommend leveling as Discipline until you are a high enough level to take the Shadowform talent in the Shadow tree. Once you are able to get shadowform, respec into shadow immediately. While leveling, you will be putting as many DOTs on your enemies as possible (Shadow Word: Pain, Devouring Plague, Vampiric Embrace), and then hitting them with Mind Blast and Mind Flay. When you get closer to 85, you will get a spell called Mind Spike. At this point, it is possible to spam Mind Spike and Mind Blast to kill mobs, and the choice is up to you. In either case, you should be trying to time Shadow Word: Death to kill the mobs you are fighting when you cast it, so you take full advantage of its effects. 

-- PVE as a shadow priest. 

      Shadow Priest has had a wild ride as far as the utility of the class is concerned, but these days in Cataclysm, Shadow Priest is one of the top DPS. When in a raid, there is a relatively simple strategy to employ as far as your spells go. A usual rotation is Devouring Plague, Vampiric Embrace, Shadow Word: Pain, Mind Blast, and repeat Mind Flay until DP, VE, and SW:P start to wear off, and reapply them as necessary, all while hitting mind blast whenever it is up, and especially when you have shadow orbs up. Some people like putting Shadow Word:Death in the rotation when its off cooldown, and this is not a bad strategy, but it works best if you have the talents and glyphs to buff Shadow Word Death a bit.   If you find yourself with several mobs to kill, putting DOTs on a few of them and then Mind SPike/Mind Blasting down a separate one will provide a very high amount of DPS. It is important to watch your threat here and it is also important to make sure that you don't Mind Spike the targets you've already DOTted up, since Mind Spike clears the DOTs.

--PVPing

      As far as PVP goes, the strategy is somewhat different than PVE. In PVP, your role will primarily be a single target DPS class, with lots of crowd control available. It is important to spec into Silence, Psychic Horror, and improved Psychic Scream, as well as to glyph to make all of these abilities as potent as possible. A basic strategy(there are many) for actually fighting in pvp is to first CC your target in some way, usually with Silence or Psychic Horror. While they are briefly CCed, you should DOT them up, and then proceed to hit them with MB, SW:D, and Mine Flay. Don't cast mind Spike on your DOTted targets. Another strategy is to use Mind Spike and Mind Blast to burn down your target, but this does not work as well if you get CCed or interrupted, because then your damage stops completely, while with the DOTs, it keeps ticking away. In PVP, it is important to use your Psychic Scream ability successfully, whether it be to stop 4 or 5 people from casting at once, to provide defense, or to provide utility, such as protecting your flag. Mine Control is also somewhat useful in PVP, but it requires very specific situations, so I will not mention it here.

Well, there you have it. A very basic guide to playing Shadow Priest. I have not included the finer points per say, but this will definitely be a decent start for any aspiring Shadow Priest. For the horde!