Who can create a MAC? Who can verify a MAC? I have read many answers but I cannot get the basic explanation. There's no need for full details. I just need some basic information about who can create a mac and verify it.
Anyone who holds the key can create a MAC. For any secure MAC it should be computationally infeasible to create a MAC without knowledge of the key.

By the correctness of a MAC, anyone who holds the key can verify it. In pretty much any practical MAC, the key is also needed to verify, but this is not something that's actually implied by the functionality or security definitions.