Step 4: Connect the Nexus device to the computer and click allow USB debugging on the device. Step 3: Enable USB Debugging: To enable USB Debugging go to Settings > Developer Options > Enable USB Debugging. Step 2: Enable Developer Mode: To enable navigate to device Settings > About Phone and tap on Build Number seven times until a dialogue box appears 'You are now a developer'. This program will run on PC to connect Nexus device through USB cable to flash Android OS. Step 1: Download and install ADB and Fastboot to your computer correctly. Step-by-Step Installation process of Android 5.1.1 Lollipop for Nexus using ADB Sideload