You can watch Netflix and YouTube on Roku by selecting them from the home screen, but you don't have to. If you're already watching something on your phone or tablet, you can cast your content and pick up right where you left off. The process is the same for both apps, and it could prove useful if the TV suddenly frees up.
1. Open the app on your phone or tablet.
2. Press the Cast button.
It's the button that looks like a TV screen in the upper right corner.
3. Select your Roku device.
4. Watch your content.
Your media will appear on-screen, and you can control it either from your phone or your remote control.