Starting a band can be as easy as just jamming with some friends or as complicated as you make it. Be sure to know what you want to accomplish with your band and that will help you determine what needs to be done.
Bands can be to just get together with a few friends and have fun.
It can be to play clubs to get free beer and score with the chicks and dudes. It may be to write original songs for personal satisfaction or to get that major record deal. You have to know up front what you are trying to do with it. Don't just let it fall together because, it WILL fall apart usually as quickly as it came together. You may want to form a band or just join a band.