How to ssh to a server using another server?

I've been doing a lot of server side stuff lately and I'm loving working on the shell and learning a lot of new shell commands too. Here is a quick and short update on what I've learned yesterday (10th Oct).

We have a client who has a staging server with IP restricted so every time I connect I had to ask them to add my IP to their firewall, that stink. So I wanted a better approach so I sent them our dev server IP to them so he can add the IP to their Firewall and I can access their server via our dev sever.

Here is the command to use to tunnel through another server:

ssh -t username@SERVERA ssh username@SERVERB