By default, ubuntu MATE comes with ssh installed but disabled. So there are a few steps to setup ssh to your raspberry pi.
openssh-server is installed with
sudo apt install openssh-server
check ssh status with
sudo systemctl status ssh
if it is
inactive, you can start it with
sudo systemctl start ssh, and/or automatically start ssh on boot with
sudo systemctl enable ssh
go to settings -> login window and set automatic login to your robot's username.
For more information, here is a useful site that explains it more