It shows how to create multiple SSH keys for accessing multiple remote servers from a single local machine.
The post would use git hosting services: Github and GitLab (which allows for SSH connection to hosted repos), to illustrate the steps. Say for example, at work you use Gitlab but for personal projects you use Github, and you want to be able to use SSH to interact with these two services from the same local machine.
Although Git hosting services are used here, the steps outlined is in no way tied to these git hosting services, it works just the same for any SSH connections.
First Step: Generating the SSH Keys.
The git hosting service would provide you the instruction for generating an SSH public/private key and how to add the public key to your account. For examples see Github's instruction.
It basically involves running this command:
ssh-keygen -t rsa -C "Comments you want attached to the key"