what is the Action-Mapping XML file?

need to get a few things cleared up. I have been looking for an answer for this one, but I can't seem to find a good answer to my specific questions I read that

" Controller Servlet works as a dispatcher transmits all the received HTTP requests to the relevant Actions.

and I have read

"Use Action-Mapping XML file to execute the action"

can you explain the different and is there a relation between Controller Servlet and Action-Mapping XML ? and the reation between Controller and Servlet ? and what happen when user click to button in view does they execute Action-Mapping XML ?