How to set up a firewall on Ubuntu 18.04 ?

By default Ubuntu has a built-in firewall known as UFW(uncomplicated firewall). For inexperienced users, It it difficult to use iptables in order to properly configure a firewall. UFW makes the configuration of a firewall very easy since it is a simple interface for the standard iptables in Ubuntu. Although it does not offer the powerful features of iptables, UFW allows to carry out basic firewalls tasks via its simple-to-use graphical interface.