I think a manpage hardly qualifies as a response for someone that doesn't understand what they are doing.

You can manually kill process from terminal in a variety of ways.
Two common methods are kill by process ID# and killall by name.

Keep in mind that process IDs change per instance and that killall requires the exact name of the process.

$ kill 1234

or

$ killall metacity

To list all processes
$ ps -aux
if you wanted to see if Metacity was running
$ ps -aux | grep metacity
then you can kill it
$ killall metacity
and later on start the process again
$ metacity &

You can also see what's running with
$ top

EDIT: I'm just assuming you are using metacity in gnome but you may be using something else or a combination. It may even be asking you to kill hildon. *walks away*