Check out example codes for "how to check listening ports on a server". It will help you in understanding the concepts better.

Code Example 1

$ sudo netstat -plnt
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address               Foreign Address             State       PID/Program name
tcp        0      0 0.0.0.0:3306                0.0.0.0:*                   LISTEN      3686/mysqld
tcp        0      0 :::443                      :::*                        LISTEN      2218/httpd
tcp        0      0 :::80                       :::*                        LISTEN      2218/httpd
tcp        0      0 :::22                       :::*                        LISTEN      1051/sshd

Code Example 2

sudo ss -tulwn | grep LISTEN

Learn ReactJs, React Native from akashmittal.com