I've made it easy for you guys starting out. Setting up your garage is easy. Your going to want a Build Sheet of each car you have (you can copy the template I provided below), and a Bank Statement keeping track of all your money transactions. Everything after that is totally up to you. You can add a section for photos of your build if you wish, also maybe make a Story for your stay here at BNB. Its up to you! For a complete garage thread to look at for ideas, look at my garage, Falken's.
There is two different Build Sheet templates. One is for PD cars, and one is for SP Mod cars. You may edit the template once you have your car, if you have more/less parts than on the sheet.