How do you redirect the url without the www.
 

I just purchased two domain names from namecheap and added them to the hostgator host. I am trying to redirect one of the domain names to go straight to the other domain name. I added both domains and used the redirect domain and it works only when you type the full name.. like www.mysite.com would take me to www.mymainsite.com, but mysite.com doesn not take me to www.mymainsite.com, i put in the redirect when i added to redirect with www. and without but it doesn't redirect unless you type in www.