How to kill processes in Linux

A useful article on the above although he doesn't seem to include everything.
For example "pkill" is not mentioned. This is good as you don't need to know the PID and it will kill all instances of whatever you want to knock out.
So "pkill opera" will kill all opera stuff thats running.
He also doesn't mention that many Linux OSes have "Forcequit" applets that will do the same thing in a GUI sort of way.
However, although I tend to more use htop than top, it seems to be easier to stop top than htop. To stop top, just gets its PID, then type "k" to kill it and enetr the PID.
This doesn't seem to work for htop.