First, you must go to the Roku channel store by scrolling to the left side of the screen. 
After that, choose streaming channels and navigate to the web video category. 
Look for the Twitch app, if you cannot find it there, then go to the search bar. 
Secondly, input the app’s name in the search bar and choose it from the result. 
Moreover, highlight the app and then choose the Add channel option. 
This will download the app on your streaming device. 
Further, access the Twitch channel app and get the activation code. 
Open a web browser using a computer to go to the activation site. 
Visit twitch.tv/activate and enter the code for activation without any mistakes. 
Finally, hit the Activate option to start the activation process and stream all your favorite games.