You can get the list of running processes by running
In the first column you have process owner, in the second - process number (PID) and in the last one - program name. To kill one of them type
(you need to be logges in as the process owner or as root).
For example, take one line of ps aux output:
mara 2227 0.0 0.3 2780 1648 pts/1 S 12:19 0:00 /bin/bash
To kill it, run
Note that it's sometimes normal when you're logged in multiple times to see your login name printed more than once by 'users'.