I’ve been wanting to get a top and was wondering what string you use, is it yoyo string or is it special top string?

Any top you purchase should come with the proper string.
It is not yoyo string.
Cotton is best to use for spin tops.
I suggest you purchase a ball of #24 Multi-Purpose Twine (Twisted Cotton) from an ACE hardware store.
It’s a good general all-around string for most tops.