Please learn how interest works before getting a credit card. I don't know what your mom has told you, but the concept of interest itself is not that complicated. In the case of credit cards, it basically means that if you owe money on your card by the time the company sends out your monthly bill, you may owe an extra percentage on top of what you already owed before depending on how often the interest is added on (and of course what the interest rate on your card is). Interest can be compounded once a month, once every three months, once a year, etc. I'm not sure what the normal period is for a credit card.
At any rate, just be sure to do some research of your own sometime and not just go off the word of your mom and some dudes on a metal forum.
Uh, I'm pretty sure that's false. Charging to your card and then paying off the charge promptly shows people that you're responsible with your borrowing and know how to limit yourself. It's the same reason bank loans can build your credit if managed properly.