There are basically three types of bleaches you can buy. First, you can buy bleach powder and 20, 30, or 40 volume developer separately. You simply mix the powder and developer in a non-metallic bowl and apply to your hair.

If that seems too complicated, you can always buy a bleach kit. Just about every hair dye company has one. They all consist of basically the same thing: Bleach powder, developer (usually 30 or 40 vol.), gloves, mixing tub, tinting brush, and a processing cap. Again, you just mix the developer and powder in the provided tub and slop it on your hair with the provided tint brush (or your gloved hands).

The last type you could get would be from a major dye company such as L'Oreal or Clairol. With those bleaches, the developer is already in a bottle. All you have to do is add the powder, and sometimes a "blonding gel". Then, shake until smooth (sounds tasty, doesn't it?). The last thing is squirt on your hair and spread around with your gloved hands.

I've found that the kits from dye companies such as Manic Panic, Special Effects, and Beyond the Zone work best for me because I don't have to rummage around my house for a plastic container, cap, and gloves. But recently I've started using Feria's Extra Bleach Blonding because it creates lots of highlights in my hair, and when I color it, the highlights show up through the dye.

Any store that sells dye will sell some form of hair bleach. If you're looking for powder and developer separately, you'll have to go to a beauty supply store. Hot Topic sells bleach kits from Raw, Special Effects, and their own. Most online shops will sell them, too.