How do you install free e-mail on your domain? Like the free e-mail service available above.

That depends on your host :) If you've got a free domain, (like .tk) you can set it up from the Control Panel there. If you are using a .com and have paid hosting, contact your host about it. It should already be set up, try yourdomain.com/cpanel/!

I have a .net domain. I know how to access my webmail through my cpanel, but I'm wondering how to give my hostees access to webmail and how to change the templetes and stuff. I want to install something like what lissa has installed above.

That I do not no. Again, contact your host and ask him/her about it. Its probably an apache module or something.