If you know the name of the process, you don't need to know the pid# If you do not know the pid#, which are often obscure, you can just type /IM after the word taskkill. This indicates your going to call it by its image name. So Firefox is Firefox.exe, and Photoshop would be Photoshop.exe. Much simpler.
Also throwing in a /f forcefully quits the program. Kinda like opening the task manager. But you will lose unsaved data.
You could just do:
taskkill /IM notepad.exe
or you could do this
taskkill /F /FI "USERNAME eq Bob"
Which would kill all processes opened by the user bob. Kinda neat if your computers freezing up and you can access the cmd prompt.
Type "taskkill /?" for a menu with all the options.