Do you plug the ps3 Ethernet cable back of the PC?

No that is the same internet input that is on the PS3 and not an output to provide the internet to other devices. Just how does your PC get the internet. Mine got it from an ethernet cable that ran from my Comcast cable modem to the PC. Some people have wireless for the PC and you can use that same wireless for the PS3. All the ads showing features for the PS3 state Online connectivity requires broadband internet service and network devices such as a DSL or cable modem. Most people who have this also require a router and an ethernet cable or a wireless router to allow connection of more than one device to there internet service. The ethernet cable plugs into the back of the PS3 and goes into a router or a modem and provides a stronger more constant signal for PS3 online connections and is called a wired connection rather than WiFi.