This system consists of two routers of the same type or not (at least both from Asus), which will be connected together resulting a larger area of signal, and higher speeds on devices which had lower signals on a single router.
You need one of the routers to be connected to the internet via a ethernet cable, and the other will communicate (together with his clients) through the first one. Please be sure which one is connected "outside" on the internet (the main router, we'll name it "first router"), and the other one, which will communicate through the "first router" (this is going to be named the "second router")
Here is a guide that will let you know everything that you need to do (with pictures): http://www.4shared.com/file/229730229/3f658e18/ASUS_Wireless_Router_WDS_Confi.html
The main things are:
- both routers must be set to operate into "Hybrid" mode
- both routers must operate on the same Channel
- both routers must have the same security method and the same password
- their LAN ip's must NOT be the same!
- first router must have DHCP server enabled, while the other (second one) doesn't
- first router must have normal internet settings (depending on how you connect to the internet), while the other must have "automated IP" settings.
- after you are sure that you know their LAN ip addresses, give them the same SSID (name)
Now you should be able to get on the internet on wireless or via any LAN port from both routers.
Method implemented for Asus WL-520GC <--> Asus WL-520GU by me and works perfectly. Good luck!