How do I fix a hole in an interior block wall?
This wall does look more like plasterboard/plaster &amp; lathe than it does any sort of cinder block/Concrete Masonry Unit (CMU). The wall cavity just isn't thick enough for a CMU before there's what looks like a finished wall on the other side.
If that's the case, I'd suggest cutting back the rough edges until you find some sort of stud (on each side), then do a simple plaster board repair on the wall. There should be plenty of examples here of how to do that, but if you can't find an explanation that makes enough sense to you, ask a new question and indicate your specific stumbling block.