There are several different styles. Cut on Contact, replaceable blade, mechanical and low profile.

Cut on contact heads are just like they sound. The sharp edge goes all the way to the tip. These are just superb, all around heads. Especially for lower poundage shooters who need the added penetration. Personally, my broadhead of choice is the Magnus Stinger, which is a COC.

Replaceable blade heads are also great. The infamous Muzzy falls into this category. While the COC heads can be resharpened, if the blades here are dull you simply replace them. Nothing to it. Most have a Trocar tip, or some variation thereof, and are designed to punch through bone. Some of these heads are not all that good on a higher speed bow.

Mechanicals are heads that have the blades folded up and expand upon entry into an animal. The biggest draw to these is they are super easy to get flying good. Basically, just screw them on and shoot. There are several drawbacks, and several advantages. First, they've been known on occasion not to open properly. They sometimes deflect. They burn up alot of KE upon entry as well. Most outfitters don't allow them. But they are just fantastic for turkeys. I use a Rocket Hammerhead because of the 2" cut I get w/ them. Oh, that's another advantage, they have a much larger cutting diameter, generally speaking.

Low profile heads are ones such as Sonic, Slick Tricks, and the likes. They are short, low profile w/ generally less than 1" cutting diameter, but they fly like darts. Good all around heads as well.