"Hm, well...it's basically an ability you're born with, or get young. It can vary across types, so sometimes it's something you can do, but sometimes it's a physical trait, too. I have a classmate who has a tail, a classmate who is invisible, and then someone else who can run really fast because he has engines kinda built into his legs...? So, those are all sort of physical. But then I have classmates who can emit or control things like electricity..."

So there's a huge variety. Izuku is always happy to ramble about Quirks, even if he's having a crash course in explaining them to other people.