A firewall is hardware or software that controls inbound and outbound traffic of a server. In other words, it is a fairly important element of server security. If we have a server that connects to the Internet, it is a good idea to set a Firewall up.
You can set up firewall manually on your server, make sure to check these tutorials for more details:
If you configured your firewall and can no longer login to your VPS, all you need to do is Reset Firewall straight from your VPS Management section.