terminal operation in git vscode, how to do after eval

I'm very sorry to those who are kindly commenting on my series of messes, but I'll start over once, around 24:23 (https://www.youtube.com/watch?v=RGOj5yH7evk&t=1511s)
Now I don't understand it again.There are two things I would like to clarify.
①$eval "$(ssh-agent-s)" was not recognized as vscode, and stackoverflow said that it would be good to do it with Git Bash, and when I tried, the Agent pid was displayed properly.However, should I use Git Bash or vscode after that?

それAnd what should I do next?Should I change id_ed25519 to testkey?
If you created the Adding your SSH key to the ssh-agent Ad Add your SSH private key to the ssh-agent. key under a different name or add an existing key with a different name, replace the command id_ed25519 with the name of the private key file.

$ssh-add to /.ssh/id_ed25519"
https://docs.github.com/ja/authentication/connecting-to-github-with-ssh/generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent