Data is passed through ports on computers so packets are sent and recived at some ports on our computer that are open with pfsense we can open and close specific ports that are required because opening unnecessary ports leads to security issues and are a lot to manage.
Some Common ports
World Wide Web access (using the Hyper-Text Transfer Protocol, or HTTP)
E-mail (using the Simple Mail Transfer Protocol, or SMTP)
File transfer (using the File Transfer Protocol, or FTP)
Translating a host name into an Internet address (using the Domain Name Service, or DNS)
Remote terminal access (For example, Telnet, Secure Shell, RDP, or VNC)