URL re-direction?
 

I have seen this done on a couple sites I already have. But, since this the first vBulletin site I'm doing myself, I guess I'll have to ask.
When someone types in my URL, how is it they will get re-directed to the full path necessary? What is it I have to do?

http://mywebsite.com - to be re-directed to:

http://mywebsite.com/forum/index.php

And I notice on some sites that you type in the URL and it starts properly, but shows no re-direction. How is that way done?
JD in KC