's interface is carefully optimized for both menu and keyboard use—with many convenient ergonomic features, including some that are not immediately visible from menus.
Multiple Click —
select larger and larger subexpressions
, Alt+( —
enter matched brackets: 
copy down an input line ()
copy down an output line ()
search for help on the name selected, or to the left
bring up a new instance of the help viewer
evaluate the selection in place
copy as plain text
toggle cell groups open/closed
, Shift+Ctrl+} —
open/close all cell groups
immediately close a notebook without saving
create a new notebook, package, slide show, etc.