WHAT IS A PORT ?
We can say that A port number is a way to identify a specific process to which an Internet or other network message is to be forwarded when it arrives at a server.
A port number uniquely identifies a network-based application on a computer.A port number is the logical address of each application or process that uses a network or the Internet to communicate. In a server, more than one user process can use TCP at the same time. To identify the data associated with each process, port numbers are used. Port numbers are 16-bit, and numbers up to 65535 are possible.
Here are some Important port numbers for you :
20: File Transfer Protocol (FTP) Data Transfer
21: File Transfer Protocol (FTP) Command Control
22: Secure Shell (SSH) Secure Login
23: Telnet remote login service, unencrypted text messages
25: Simple Mail Transfer Protocol (SMTP) E-mail routing
53: Domain Name System (DNS) service
67and 68: Dynamic Host Configuration Protocol (DHCP) servers use UDP port 67 to listen for requests while DHCP clients communicate on UDP port 68.
69: TFTP(Trivial File Transfer Protocol) TFTP offers a method of file transfer without the session establishment requirements that FTP uses. Because TFTP uses UDP instead of TCP
80: Hypertext Transfer Protocol (HTTP) used in the World Wide Web
88: The Xbox Live Internet gaming service uses several different port numbers including UDP port 88.
110: Post Office Protocol (POP3)
119: Network News Transfer Protocol (NNTP)
123: Network Time Protocol (NTP)
137/138/139 NetBIOS
143: Internet Message Access Protocol (IMAP) Management of digital mail
161and 162: Simple Network Management Protocol (SNMP)
194: Internet Relay Chat (IRC)
389 Lightweight Directory Access Protocol (LDAP)
443: HTTP Secure (HTTPS) HTTP over TLS/SSL
The registered ports are those from 1024 through 49151. IANA maintains the official list of well-known and registered ranges. The dynamic or private ports are those from 49152 through 65535. One common use for this range is for ephemeral ports.