One of the most useful functions of the .htaccess file is to redirect requests to different files, either on the same server, or on a completely different web site. It can be extremely useful if you change the name of one of your files but allow users to still find it. Another use (which I find very useful) is to redirect to a longer URL, for example in my newsletters I can use a very short URL for my affiliate links. The following can be done to redirect a specific file:
Redirect /location/from/root/file.ext http://www.othersite.com/new/file/location.xyz
In this above example, a file in the root directory called oldfile.html would be entered as: /oldfile.html
and a file in the old subdirectory would be entered as: /old/oldfile.html
You can also redirect whole directories of your site using the .htaccess file, for example if you had a directory called olddirectory on your site and you had set up the same files on a new site at: http://www.newsite.com/newdirectory/ you could redirect all the files in that directory without having to specify each one:
Redirect /olddirectory http://www.newsite.com/newdirectory
Then, any request to your site below /olddirectory will bee redirected to the new site, with the extra information in the URL added on, for example if someone typed in:
http://www.youroldsite.com/olddirecotry/oldfiles/images/image.gif
They would be redirected to:
http://www.newsite.com/newdirectory/oldfiles/images/image.gif
This can prove to be extremely powerful if used correctly.