Hi, I don't think its a dumb question. It can be confusing when applying for your first job (it was for me).
First you will have to fill out a job application. You will probably be asked to include a few personal references (sometimes non relatives), so bring their contact info (address and phone number) with you when you go to fill out the application. You may also be asked for your ID and social security card, so have that, too.
After you submit the application, hopefully you will be called for an interview, or called to let you know you have been hired. The last time I applied for a job at a fast food place, I didn't have to go through the interview. I was called by the manager to let me know when they wanted me to start.
Good luck!!!
[edit] I just read that you are 15 1/2. Be sure to check to see if you need to secure a work permit first. I did at your age.