first time maintaining a real life job

Almost a month ago I contacted a woman that would likely give me a job at a jewerly shop. The most I knew about this job was that I was gonna work on the weekends, that sounds fine, I like resting a lot since I'm tired all the time, but it couldn't be so bad, y'know?
I was hesitant at the moment, I didn't really know if I wanted the job or not, but something like that, it didn't sound so hard, like working on a pizzeria's kitchen... Oh, God, what an awful experience.

Things now are better, I'm less stressed about it at least. I've gone to work twice already (It's actually just Saturdays!), it's tiring but I get to be sitted down, so it's nice. The worst part in my opinion is NOT KNOWING A LOT (ANYTHING?) ABOUT JEWELS, that's definitely the worst worst part, but I'm still new so I can better, and I've been trying really hard not to cry sometimes, I'm quite sensitive to being such a mess in general.

I'm already 20 but I can't do this things that should be easy, or at least easier. My time at that pizzeria were truly awful, I don't like sharing that experience anymore, it wasn't so hard but I was really weak then lol I still think I am very weak as a person, mentally, but if I've been able to do it this far maybe I really do have a chance to be a functional adult in society one day.