what is mac cleaner and do i need it

Never heard of it.

If you need to clean your Mac do so according to the instructions here:

http://support.apple.com/kb/HT3226

If you are asking about "cleaning" apps, do not use them. Same goes for "optimizing" or "speed up" or "clean up" or "tune up" or similarly named junk. You do not need them and they are likely to cause problems.