1. Install openssh-server
$ sudo apt-get install openssh-server
2. Check the SSH status, it should be enable
$ sudo service ssh status
If not start the ssh service.
$ sudo service ssh start
3. To change some settings like listening port, edit the config file at:
/etc/ssh/sshd_config
After editing the sshd_config, restart the ssh service.
$ sudo service ssh restart