There are three kinds of hitches: bumper mounted, frame mounted, and load equalizing.
Bumper mounted hitches are those which attach solely to the vehicle's bumper. Many states prohibit towing with this type of hitch when it attaches to the vehicle's stock bumper, since it subjects the bumper to stresses for which it was not designed. Aftermarket rear step bumpers, designed for trailer towing, are acceptable for use with bumper mounted hitches.
Frame mounted hitches can be of the type which bolts to two or more points on the frame, plus the bumper, or just to several points on the frame. Frame mounted hitches can also be of the tongue type, for Class I towing, or of the receiver type, for classes II and III.
Load equalizing hitches are usually used for large trailers. Most equalizing hitches are welded in place and use equalizing bars and chains to level the vehicle after the trailer is hooked up.
The bolt-on hitches are the most common, since they are relatively easy to install.
Check the gross weight rating of your trailer. Tongue weight is usually figured as 10 percent of gross trailer weight. Therefore, a trailer with a maximum gross weight of 2000 lbs. (900 kgs) will have a maximum tongue weight of 200 lbs. (90 kg). Class I trailers fall into this category. Class II trailers are those with a gross weight rating of 2000-3500 lbs. (900-1600 kgs), while Class III trailers fall into the 3500-6000 lb. (1600-2700 kg) category. Class IV trailers are those over 6000 lbs. (2700 kgs) and are for use with fifth wheel trucks, only.
When you've determined the hitch that you'll need, follow the manufacturer's installation instructions exactly, especially when it comes to fastener torque specifications. The hitch will subjected to a lot of stress and good hitches come with hardened bolts. Never substitute an inferior bolt for a hardened bolt.