My friend is a minor like me, we're only 15, but he has a credit card that he uses to buy stuff online, so he doesn't have to use his mom's credit card. I was wondering where to get something like that, like a credit card that you fill up with money and you can use it anytime.

You can but you parent will have to co-sign for you but you can get one just by searching online with google those types of cards are called visa gift cards or rechargeable visa cards