how do i clean my mac book air safely, and what is MacKeeper and is it bad for my mac?

A Mac does not need any 'cleaning' that is automatically done by the OSX.

Mackeeper is the Ebola of so called 'performance' and 'cleaning' applications. Do NOT install it:

https://discussions.apple.com/docs/DOC-3691

Ciao.

http://www.reedcorner.net/beware-mackeeper/

http://applehelpwriter.com/2011/09/21/how-to-uninstall-mackeeper-malware/

ASC user tip on Mackeeper by Klaus1 - https://discussions.apple.com/docs/DOC-3022 = https://discussions.apple.com/docs/DOC-6221 = https://discussions.apple.com/docs/DOC-3691 (3 copies!)

It's best to describe the functional problem, if you have one, in as much relevant detail as possible, rather than to say what you think is causing it or how you think it should be solved.