Uninstalling progrms?

[Kumara]

Hi all,
I'm a newbie of Linux, for practicing installing rpms and tar.gz files, I
installed a lot of unnecessary programs even asterisk. but many times, I
could not launch many programs after installing or the particular program.
because I don't know how to do it. now... my system is slow and run with lot
of stucks/non-responsive times. I want to practice some more before making a
clean installation again. could somebody tell me to practice some good
commands or run some good programs as a newbie in Linux including
uninstalling programs?
Thank you in advance
 Mohan