Someone explain credit to me

I understand the jist of it I think. You buy something with credit and that is basically like using the banks money and over time you make payments towards it.

Do you get to choose how much you do monthly until it's paid off? Or do you not have a say it that? As soon as I have a good chunk of money in savings and I have a steadier job I want to start building credit since I have none as of none, but before I do that I want to make sure I understand completely.

I don't exactly need these things, but you have to build credit somehow right? Why not spend it on items you have been wanting for a long time. I want to get a nice new bed and frame, as well as a new TV since this one the sound is going out. That can easily add up to $1500. I won't be doing this until I'm sure I can make payments on time each month.

My lease is up next September and I figured I can get into a better place if my credit is good