Understanding REST Verbs and its relationship with CRUD

I used to believe that REST verbs mapped to CRUD operations more or less like this:

GET -> Read
DELETE -> Delete
POST->Insert/Update
PUT ->Insert/Update

Yes, I mapped both POST and PUT map to the same CRUD operation, but now I am not that sure this mapping is completely right…

I have learned that the difference between POST and PUT is the URI, in PUT the URI identifies the entity enclosed with the request (the entity you wan to Insert or Update), while in POST the URI identifies the resource that will handle the enclosed entity.

So, POST is like saying "Resource X, do something with this Entity", while PUT is more like "Insert/Update this Entity as Resource X"

So POST is more like “Tell ‘X’ to do something with ‘E’” and that has really no direct mapping with a CRUD operation… of course, a POST, internally, can do one, or many of the CRUD operations using the data of the entity that is being passed to it as a parameter… Does that mean that POST maps to all CRUD operations?

I guess I need to learn more about this…