Yes as Mr. Wishbone said, you could do it by the two way.
Here :
1st by editing .htaccess :
add this code :
Redirect /index.php http://example.com/forums/
or you could also keep it as Wishbone said :
Redirect /index.html http://example.com/forums/
you could keep either index.html or index.php doesn't really matter.
2nd : cPanel
In your cpanel, browse to Domains > Redirects
Then select the domain you want to redirect (by default it would be "**All Public Domains**") :
Just select the domain you want, or leave it as it is if you don't have any other domains in your hosting.
and enter the domain it should be redirect to below it.
Note : Remember to select the redirection option of www.redirection :
Its clearly written what every option means.
So no need to explain.
And Wild card will redirect all files within a directory to the same filename in the redirected directory.
So upto you to do it or not.
Hope this helps