Type this command

ssh-keygen -t rsa -C your_email@gmail.com

After only press Enter without typing anything and then It will ask you to enter a password.

You can discover the public key by typing

cat id_rsa.pub

Copy the result of the command and past inside your github

At the end is important to add the private key to you local agent.

ssh-add --apple-use-keychain ~/.ssh/id_rsa