php redirect based on information after .com/THISINFO

I have researched previous questions and either I don't understand the answers or I'm too tired.

Either way. I want to 开发者_如何学JAVAdo this..

someone enters blahblah.com/STUFF into their browser

There is no blahblah.com/STUFF file in the directory, but I want to pass STUFF to a file in the directory.

Just thinking out loud here, someone does blahblah.com/STUFF how do I post STUFF to a php file in the directory? Then with that posted variable of STUFF I can redirect within the PHP file to another page.

Some posts say have .htaccess in the directory, but I don't understand their syntax.

Thanks

RewriteEngine on RewriteRule ^STUFF /index.php