I'm assuming that you've already configured port forwarding and are able to get through to the machine at work.
Otherwise, even after following my answer, you won't get very far.
The SSH server is not installed by default.
You will need to install it by running these commands in a terminal (ctrl+alt+t) on the machine you wish to connect to:
sudo apt-get update
sudo apt-get install openssh-server
Then you will be able to connect normally by running:
#Replace user & IP accordingly
However, in that state you have a security risk.
As Oli has noted here,
You need to harden it from the standard setup. I've gone through
several suggestions on my blog but at the very least, I'd suggest:
- Key-based logins. Disable password logins.
- Move it off port 22. Use something crazy-high, in the 20000-60000 range.
fail2ban to ban people who do find it and try to brute it.
They take about 10 minutes in total and you go from a 1/10000 chance
of being broken in to a probability so small, there isn't enough paper
in the world to write its fraction... Assuming you're careful with
your key, it has a password of its own and you don't trumpet your
credentials all over the net.
If the computer is behind a router, you'll also want to do some port
forwarding. This is router-specific so I'll just direct you to