Question over the app

Ok, so I downloaded GBA4IOS off IEmulators. For free. However, it said something about a "Build Store" for 10 bucks a year. Is it optional? I'm just a teenager who wants to play old childhood games on his phone. Will I be charged since I have GBA4IOS downloaded? I only downloaded one game off the web, and that's Pokemon Clover. This is really making me worried, as I don't have a credit card and stuff.

EDIT: question has been solved.