ssh
ssh allows for secure remote access to servers or other computers over insecure networks (including the internet).
getting started with ssh
While there is extensive documentation on ssh commands and related commands such as scp (for copying files using the ssh protocol), the following Wiki page will probably get you started pretty quickly:
ssh keys
ssh key files are a great way to set up safe ssh connections, and if properly set up with your operating system keychain, you can save on a lot of password typing. There's a great guide for generating and setting up ssh keys that you can quickly work through step by step. No need to remember any of this by heart, just look it up when you need it.