There are three basic types of wood drill bits. Wood drill bits are, obviously, used for drilling wood. Special wood drill bits are required for larger holes to be cut with greater accuracy.
The first type of wood drill bit is a lip and spur bit, which are also known as dowel bits. These drill bits are like standard twist drills but have a singular sharp center point and two outer cutting spurs. Because they have the single center point, it provides for a precise placement and the spurs provide a very clean hole. The lip and spur bit is particularly useful in dowel work where a precision hole is necessary for an accurate fit. Lip and spur bits are available in sizes from 3 mm to 30 mm diameters but the larger sizes of drill bits are quite expensive. Smaller sized lip and spur drill bits often come with dowel kits and usually come with an adjustable collar so the hole depth can be determined more easily. They also often come with indexing inserts, which are inserted into the hole to give you a center for drilling.
Another type of wood drill bit is a flat bit. Flat bits have a center point but have a flat cutting edge and look similar to a spade. A sharp, flat bit will quickly cut a clean hole. These bits can be sharpened after use with a file. Flat bits are relatively inexpensive because of their uncomplicated construction. Flat bits are available in 6 mm to 38 mm sizes. A pumping action is required when using a flat bit to remove excess sawdust to help avoid their tendency to wander when drilling thick timbers. Some varieties of flat bits have a screw style thread instead of a center point to help pull the drill through the timber.
Auger bits are another type of wood drill bit that look like corkscrews. Auger bits have a wide chisel-like cutting edge which gets rid of the excess waste sawdust while you are working, and one outer spur which cuts into the wood in front of the cutting edge to produce a very clean hole. The deep coiled groove helps the waste sawdust to be removed quickly. Auger bits are usually slower drilling than flat bits, but thusly produce a cleaner hole in the wood. Because of the length of the corkscrew, the hole in the wood will be more precise. Auger bits are available in lengths of at least 100 mm up to 450 mm and in diameters of 4 mm to 30 mm. Auger bits can also be sharpened with a file.
About Forstner bits, you may read here.