How to add something to start of url using htaccess?

I have seen sites that when you login it will look something like...

 .example.localhost/blahblah.php

how is this possible with htaccess?

Any ideas

Do the files have to be place开发者_如何转开发d in a seperate folder??

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It's called sub-domain.

It has more to do with the DNS but htaccess can be used to modified its behavior.

Ie, point different sub-domain to the same folder.