How to mask a url

I am a Linux System Administrator and definitely not a webmaster. But for some reason I was given on this kind of task. I’ve been searching on Google for the past few days to address this problem on masking a url. Usually, I get suggestions to do it like mod_rewrite, frameset and iframes. I already tested it all but the url just freezes.

But what we want to achieved is to have a mask url that changed its link. As an example, for a mask url like when you click the menu or any other links its just freezes on But what we want is when you click on “Contact Us”, the url now then becomes

Is this possible? I really and badly need your help. Thanks a million in advance.