Here's a TL;DR guide.
CPU
If you don't know anything, get the latest Intel i5-k processor.
MoBo
Get a Gigabyte UD3 board with the latest chipset for overclockability. Currently for Gigi, it's Z77X
RAM
Get Crucial Tactical Tracer. Or G.Skill Rip Jaw if your <16 years old.
GPU
Get the latest AMD you can afford. Nvidia is fine but I assume you're a gamer and not a 3D modeler or anything. AMD is strictly gaming. Nvidia is gaming + modeling and animation and professional stuff. For gaming, AMD will get you the best bang for the buck.
SSD/HDD
Getting a SSD is pointless unless you plan to put everything on it. Buying a small 64/128GB SSD just for your OSS is retarded. You'll only notice faster boots but on a gaming desktop, I assume the only time you ever turn the desktop off is for updates. Get a 256GB at least for your OS and core software and games, then a HDD for music and movies and pictures. For HDD, Get a WD Caviar Black or Seagate Barricuda.
PSU
EVGA SuperNova. Nuff said.
Case
Get a good case. Not some riced up piece of shit with windows and LED fans. They look nice to you and your dorky friends but they won't help on maintaining cool temps. Get a mid-tower as well. Buying full-tower is for SLI and water cooling, and if you dont know how to pick out PC parts and look for guides, you shouldn't be doing SLI or WC yet. Get some quality fans too, no cheap LED ones. Go with Noctua pls.
You won't regret the $20 price tag.
Other things; don't get a wifi adapter. If you're going gaming, you should be hooked up via ethernet anyways. Buying an expensive gaming PC when you have shitty connection is an oxymoron.