Question: how to connect my ps3 controller to steam?
Answer: Plug your Dualshock 3 in. ... 
Get PlayStation Now and install it. ... 
Re-plug your Dualshock 3, go to the Control Panel -> Devices and Printers, find your Dualshock 3 there, right-click it, choose "Game Controller Settings", select your Dualshock 3 and press "Properties". ... 
Start Steam.