The Internet Connections tool shows you:
A port number is somewhat like a telephony system extension number. Each connection between two programs has two port numbers, one for each end of the connection.
Instant messenger programs such as Yahoo Messenger, MSN Messenger, ICQ, etc need to have at least a connection to their instant messaging server at all times.
Web browser programs such as Internet Explorer and Firefox create Internet connections as needed.
Web server programs such as Microsoft IIS (Internet Information Server) or Apache open ports (usually the port 80 which is reserved for web communications) so web browsers from around the Internet can contact them and request pages.
Some malware (that means adware, spyware, trojan or virus) programs open ports and wait for somebody on the network to connect to them and give them commands. This is one of the ways a hacker can take complete control over your computer.
However, please don't panic - many programs opening ports are legit programs, which use the opened ports for legitimate purposes.