@anakaren can you elaborate more on which part you're getting stuck? Are you currently trying to sign up for Stadia? If you haven't, you can go to this following link and start your one month trial
https://stadia.google.com/
If you follow the procedure it should be self explanatory. If you're still getting confused, please reply back with more explanation and we can try to assist you more.
Have fun!
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Stadia Guides are not employed by Google. Opinions are my own.
