Question : What does the port number indicate?

Hi,

I have a problem understanding the different port number represents. I know that port 25 is for SMTP and 110 is POP3. I need to understand the different port use for. Please help.

Thank you.

Answer : What does the port number indicate?

When computer A is communicating with computer B, computer B needs to have a way of identifying what application computer A is trying to communicate with.  Computers use IP addresses to find each other on the internet, and they use port numbers to distinguish between different applications on the same computer.  

For a full list of common port numbers see: http://www.iana.org/assignments/port-numbers