The most basic C-h options are C-h c
describe-key-briefly) and C-h k (
C-h c key prints in the echo area the name of the command
that key is bound to. For example, C-h c C-f prints
‘forward-char’. Since command names are chosen to describe what
the commands do, this is a good way to get a very brief description of
what key does.
C-h k key is similar to C-h c but gives more information. It displays the documentation string of the function key is bound to as well as its name. key is a string or vector of events. When called interactively, key may also be a menu selection. This information does not usually fit into the echo area, so a window is used for the display.
C-h c and C-h k work for any sort of key sequences, including function keys and mouse events.