All you need to know about SSH to use GitHub/GitLab for ssh authentication
First, generate a crypto keypair. Hit enter 3 times to accept all defaults.
$ ssh-keygen
Then, copy the the public part of the generated keypair to clipboard:
$ cd ~
$ cd .ssh
$ cat id_rsa.pub # .pub is for public; the 'id_rsa' file is the private part of the keypair!
(long string of data shown)
Copy the string of data. Login to GitHub/GitLab and look for SSH keys under your account settings.
Paste the string and save! You are now authenticated - no need for a password anymore! Also, it's generally more secure then a short password, as long as the access to your id_rsa file is secure, which it is if your user account has a good password.
This whole magic is based on having the 'ssh agent' service running in the background. You may need to run it, especially on Windows, just type
$ ssh-agent