What happens when you didn't pay an paid app in iphone?

I didn't know that I've downloaded an paid app on my phone. So I deleted it a day after I installed it. I use my brother's apple I. D. For all I know, if you wanted to download an app that is needed to be paid you'll need a credit card but I know that my brother doesn't have a credit card.

According to some users, if you deleted an app (paid app) before you sync it to your computer. You will have to pay for it. What I don't want to pay it?

Q: 1) Do I really need to pay it
2) what can I do to not pay the app?
3) Can I even not pay the app(paid app)?
4) what will happen to my brother's apple I. D?

*haven't synced my phone to my laptop. But I've deleted the app already.

Whoever account it was on has a credit card as its required to have an account. If it was a paid app then it would have been charged when you downloaded it