If you aren't sure which command or application you need to use, you can try searching the man files.
man -k foo: This will search the man files for "foo." Try man -k nautilus to see how this works.
Note
man -k foo is the same as the apropos command.
man -f foo: This searches only the titles of your system's man files. Try man -f gnome, for example.
man -f foo is the same as the whatis command.