According to http://nl.tp-link.com/resources/simulator/TL-MR3220/index.htm
This is a simulator of your routers interface, so I can see what needs to be done.
What I'd select:
Network>Internet Acces> WAN ONLY
Network>WAN> and refresh the settings, your router should now be able to transmit the internet data to other PC's from now on.
DHCP is enabled by default so this shouldn't be a problem.
Note: You can also use the Quick Setup Wizard which will guide you through the process of setting up an internet connection from the WAN port.