The TCP port number is a 16 bit number that identifies a specific software program on the server hardware. A port represents a logical connection to a particular piece of software running on the server hardware. We have 0-65535 ports. These are just numbers representing a server application. HTTP server software runs on port no 80. telnet-23, FTP-21, POP3-110, SMTP-25. TCP port numbers from 0 to 1023 are reserved for well known services. We should not use them for our own server programs.
The TCP Without port numbers the server would have no way of knowing which application the client wanted to connect.