David,
It sounds like you want to know how to configure NAT. By "terminal" do you mean accessing the 828 via the command line interface ? If so this will probably be the most difficult way for you to configure port forwarding if you are not familiar with Cisco. You need to know how to get around the CLI interface. But if you know some basics this link will help you.
http://www.cisco.com/en/US/customer/tech/tk648/tk361/technologies_tech_note09186a0080094e77.shtml
The 800 series routers come with a built in web interface where you can configure features for your router. I would probably suggest using this to configure your port forwarding.
http://www.cisco.com/en/US/customer/products/sw/netmgtsw/ps2076/index.html
This feature should already be enabled on your router. All you need to do is go to a PC on your network and open up a web browser like IE and type in the ip address of your 828 (your PC's default gateway address most likely).
Once connected you will be prompted for a username and password the default is no username is specified but in the password field type in the enable password of your router.
Once logged in its a GUI so you should be able to follow the steps and hopefully get things going.
Daniel