Install the Steam Link app on your phone
Make sure your PC has Steam installed and running
Sign in to the same Steam account on your PC and phone
Connect your phone and PC to the same Wi-Fi network
Open Steam Link on your phone
Pair your phone with your PC
Connect a Bluetooth controller, if needed
Start Big Picture Mode or launch a game from Steam Link
Use touch controls if the game supports them
For better performance, use a strong Wi-Fi connection or USB-C Ethernet adapter