You will have to make sure that ssh is installed on Ubuntu.
From the command line (terminal)
sudo apt-get install ssh
If you use the synaptic package manager, just search for ssh and install both the client and server.
Once that is done, you can open a terminal on either computer and type
ssh <your username>@<the other computers ip address> and hit enter
if your username is the same on both computers, then
ssh <the other computers ip address> is good enough
If both of your computers are behind the same router you should have no problems, if you are trying to get from a location on the internet to your computer at home, you will have to set up port forwarding on your router and give your computers a reserved ip address (check your router documentation for how to do this)
hope that helps
cheers
