Open terminal and run 'ps aux | less'.
'ps' is the 'process status' program. The 'aux' bit are options, where a=all, u=user info (among other things, look in the first column), and x=shows processes that are not connected to a specific terminal, f.ex. started by the system without user action.
The '| less' just pipes the result from the ps command to the 'less' program, which allows you to page through the information (I guarantee that you will have more than a screenful showing up. Without less it'll just zip by too fast).
For more info on ps, type 'man ps' in the terminal. There are a million options to show you virtually everything you need.
If you need to kill a process, checkout 'man kill', and 'man sudo'. Be careful with those.
HTH