Put your band together. Traditional rock bands have at least one guitarist, at least one drummer, and at least one bass player. However, with contemporary technology it's possible to start a band by yourself, using gear like a drum machine.
Figure out your sound by mimicking your favorite bands. This establishes common influences of band members. Pick some garage standards to play like Iggy Pop and the Stooges, The Sonics, and The Trashmen. "Nuggets," a compilation of 1960s garage rock singles put together by Lenny Kaye, is a great place to start.
Write original music. Don't worry if you're recycling chord progressions from your favorite songs; there aren't that many chord progressions used in popular music anyway. Depending on the band's preference, songs can be improvised completely, or they can be composed communally or individually, written down and rehearsed.
Start recording your original material. Contemporary recording is inexpensive and not difficult. Four-track recorders, small digital recorders and personal computers with audio editing software all make for easy home recording. Audio recording and editing software ranges from free to several hundred dollars. A USB audio interface may allow for easier recording and high quality.
Play your music. Play shows wherever you can. Basements, warehouses and bars are traditional garage rock venues. You may also want to sell recordings or distribute them for free as tapes or CD's or on one of the several online distribution services.