ISP config make masked subdomain

Hello!

Can someone please explain how to make a masked subdomain?
I mean I know how to make the usual subdomain with the a record..
but i wanto make it masked in order when I write in adressbar name.domain.com so that it will stay the same unlike it is now domain.com/targetpage/

+ i would like to know how to remove/change the little adressbar icon.

Thanks!