SHAY,

Welcome to the DotNetNuke Community! Where do you teach and what subject? 

I'll try to answer your questions in the order that you asked them so as to be succint.

• You don't have to "make a login module" the login module is already in the system. If you click the login button in your skin you should see it or you can simply put " /login.aspx " after the site name and get to the login module
• Where exactly are you hosting your server? Are you with a DotNetNuke hosting company? (If not, it's a good idea to do that) ... ultimately you'll need windows hosting, a SQL database, and IIS configured and you should be able to install the application. If you don't have time or want to configure and install the application this is why it's a good idea to work with a DNN specific hosting provider... they handle all this for you
• Community version has the ability for any modules to be installed. If you would like to install E-Commerce modules on your site you can certainly do it. You can find E-Commerce modules on the DotNetNuke store. You may need to consider some things when thinking about E-Commerce. Robb Bryn has written an informative blog about E-Commerce that you should check out.
• That's a broad question... my route would be to get your site up and running and just click around in it and investigate. Don't be scared to look into the application and learn about it. It's really user friendly.  Another great resource is our Video Library which is full of video tutorials should you want to know more about any feature. We also have a Community Wiki which a good resource for finding answers too. You've found the forums already and we have a Community Exchange which is another place to get help.

Good luck and keep us posted with your progress!

Regards,

CBP