Littleberu said:The thing is, I don't know WHY I got fired. I worked there for 1 week, and I did everything they wanted me to do. They hired me as a clerk, but they made me do things such as delivery, things I wasn't prepared for. I called my boss to know the reason, but he hasn't called back yet. But man that sucks.
I can see the problem already. You had a crappy attitude. Most jobs are multirole positions. Clerk type jobs should expect to do various things such as delivery. If you "weren't prepared" to handle something as simple as delivery in a clerk type person, you're not ready to have most jobs. Clearly your supervisors saw your attitude and cut you off before you became a liability.
Edit:
Littleberu said:I talked with my boss and she said that they fired me because I didn't show enough enthousiasm and wasn't mature enough. WTF I did all they wanted me to do without complaining.
Yup, that's pretty much what I expected from your very first post. Sure, you might not have stood up and said "hey, that's not in my job description," but you clearly weren't very happy about doing simple tasks that you didn't (but should've) expected to do. Your attitude is very obvious in such situations, and you'll learn to overcome that with maturity.