1. To install it, open terminal (Ctrl+Alt+T) or log in Ubuntu server and run command:
sudo apt-get install openssh-server
2. After that, you should have SSH service enabled in your system, you may check its status by running command:
sudo service ssh status
3. You may change some settings (e.g., the listening port, and root login permission) by editing the configuration file via command:
sudo nano /etc/ssh/sshd_config
On Ubuntu desktop, you may use gedit instead of nano:
Finally apply the changes by restarting or reloading SSH:
sudo service ssh restart