Sharing Internet coection to other devices through a router

I got a Raspberry pi which is coected to router's wan port. Another win7 computer is coected to the router's lan port. I tether my phone to raspberry and want to share its coection to the other devices.

I first tried it other way around (windows pc sharing the coection) using the instructions posted on here : Setting up wifi router as a switch for Inteet Coection Sharing

I followed those instructions except that I'm using the raspberry. I believe everything is correct so far, I just need to set up the equivalent for the tap in Windows 7 "Allow other network users to coect through this computer's Inteet coection."

How do I do that in Linux?