First of all, you will need to install an ssh server on your VM before you can ssh to it. You will probably need to do this with a VNC Viewer. When your in your VM, you can install OpenSSH with:
apt-get install openssh-server
Make sure your VM is powered on before proceeding.
Access from other Redbrick servers
Note your VM's IP address from the VM Management page (not from the page that comes up after you switch on your VM). To login simply ssh to that IP address, with your VM user/pass (not your Redbrick login details). You will have set up these details when installing the operating system on your VM.
Access from an external machine
You will need to setup a tunnel to get to your VM, if you're accessing from outside Redbrick. To do this, type:
ssh -L 1337:YOUR_VM_IP_ADDRESS:22 firstname.lastname@example.org
This binds port 1337 on your own computer to your VM (on port 22, the ssh service). So to connect to your VM:
ssh 127.0.0.1 -p 1337