The .htaccess file is like a set of directions. You know how some sites have customized 404 error pages? You'd most likely have set up your .htaccess file to point at a particular directory to do that. You can do a lot of things but, for argument's sake, just imagine it like this for a minute. Like a cyber-wormhole or something...LOL
Now, if you had access to or could replace the .htaccess file, you could set up a scenario where someone wanting to visit a certain place or perform a function on a site to be redirected to somewhere else like that smoothsouthernbluesandso
ul crap that someone did. Once they get there, load 'em up with whatever you want and Bob's your uncle!
That a fast and rough explanation. Hope it helped.