Port Scanning is the process of checking which port is open or which port is locked .then you see port is opened , and you can try to communicate with victim system remotely and access their data.
* 21: FTP
* 22: SSH
* 23: Telnet
* 53: Domain Name System
* 80: World Wide Web HTTP
* 119: Network News Transfer Protocol
* 443: HTTP over Transport Layer Security/Secure Sockets Layer
* 445: microsoft-ds, Server Message Block over TCP
If these port are not secure a hacker can communicate with these port , then you hacked.
Top 5 Free Port Scanners
2. Angry IP Scanner