whats the difference between OVA and the Anime aired?

Well, anda probably already know what the definition of an OVA is, but it can be multiple things:
- A side story of an anime
- A prequel atau sequel of an Anime
- A short story almost completely disconnected from the Anime itself
- Fanservice
- An Anime series that simply didn't air on television, but stands on its own

If I like an anime, I'll usually check out its OVA if it has one. I will warn anda though, if anda watch the OVA's for every Anime anda watch, anda will eventually encounter some major wastes of time. It all depends on the show, though.