Git Bash:
ssh-keygen -t ed25519 -C ""
eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_ed25519

Powershell:
Get-Service ssh-agent
Set-Service -Name ssh-agent -StartupType Automatic
ssh-add $env:HOMEDRIVE\Users\Administrator\.ssh\id_ed25519
ssh-add -l
ssh -T git@github.com

Github:
Settings -> SSH and GPG keys -> New SSH Key