A wireless router is a Access Point with a router built in. If you need to relay traffic between subnets, a router is what you need. If you need connect wireless user to a wired network, an access point is what you need. If you need to do both, use a router. With all this said, it is usually not normal to use more than one router in a small LAN. One router (usually used to relay traffic from a broadband Internet source and an internal network) is all that is normally implemented. If you have more than one subnet in your network, you will need a router for each of those. Let me give you an example of a “typical” layout for a “typical” business LAN.
Router connected to Broadband Internet connection (LAN port of router going to LAN switches).
Two wireless Access Points connected to same group of network switches that are used to connect wireless clients (corporate notebooks and other company wireless devices).
One wireless router with the WAN port connected to the same set of switches and relaying traffic to a different subnet with strict firewall rules. This wireless router/AP is used to offer Internet connectivity to guests and visitors (who still need to be screened and given authentication credentials in order to use the “guest network”.)
I hope this helps.
Multi-Systems Programming & Communication