Editor's note: This post is part 2 of a series. Here are the links to part 1 and part 3.
Editors' note: Many routers can also work as an access point and will indicate this in its list of features. In this case the router's WAN port will work as a LAN port. In fact, for the secondary access point scenario, it's best to use two identical routers, one as the main, and the second as an access point for the far side of the house. This way you don't have to learn about two different devices.
Rule of thumb: Make sure you back up the router's configuration settings before making changes. This allows you to restore it to previous settings in case something goes wrong.