I feel like a suck at my job.

Im 17 and just got my first job at autozone a few weeks ago. I always forget how to use the software or just dont know how to do something when a customer asks for something more complex. I feel like im always depending on my coworkers to help me get through my shifts l, the other guy that also got hired the same time as me is already doing better and knows more about the job than i do. I guess I feel like im more of a burden than a blessing on my coworkers. Just wanted to post this because it's been bothering me.