$ ssh-keygen
This will generate ssh private/public key inside the ~/.ssh/.
To get the public key:
$ cat ~/.ssh/id_rsa.pub
Copy the public key and go to GitHub website. Click profile menu, Settings.
In Personal Settings menu on the left, click SSH and GPG keys menu.
On the right panel, click New SSH key button then add your public key.
Now we can access personal GitHub repositories without username and password