SSH agent forwarding allows you to use your local SSH keys on a remote host, when using it to connect to yet another host.

You can either define this in your ~/.ssh/config file with a host specific section:

Host example.com
   ForwardAgent yes

Do not simply forward to all hosts with Host *, as this will make your SSH keys available to all hosts you connect to.

You can also use it as a one off in your SSH command:

ssh -o ForwardAgent=Yes user@server