An ssh key is a way of identifying (authenticating) yourself when connecting to a server per ssh. A different popular authentication method is via a password.
Why should I use it?
When you connect to a server, authenticating via a password there are two main problems:
- Someone could intercept/crack your password, since it has to be send to the server at some point in some form.
- Someone could bruteforce or guess the password, since many passwords are commonly weak, hard to remember or used for multiple applications and then cracked/leaked.
You should start by generating a key pair:
$ ssh-keygen -b 4096
where you can specify the max length of the key up to 16384 bits.
You can then optionally protect your key with a passphrase. (Your key is basically just a file sitting on your computer and a passphrase protects your key, if someone happens to steal/copy that file).
If you did not specify a different file, the key normaly gets generated to