I am a newbie to the networking. Can u please tell me what are logical ports and how can a machine transfer or exchanges data using the ports?
Please give some websites also if possible
thanks

Internet servers provides several services such as: web,telnet,smtp,pop,ftp,... The "ports" are a way to specify what service should answer when you establish a connection to this server.

Then, when you retrieve your email, your email software will use port 110. When you request a web page, your netscape/explorer use port 80, ...

Each server software is built or configured to listen to a specific port. Some port number are reserved as per the network convention. Most known are:
20&21=ftp
23=telnet
25= send mail (smtp)
53= dns (name resolver)
80= web
110= retreive mail (pop)

Ports are part of the TCP part of TCP/IP, which uses 65,536 possible ports to bring stuff in and out of your PC, these are not physical ports, (like com 1 and com 2, or a USB port). The list that Danny gave you in the first response is an excellent example of what ports are and what they do.
www.Whatis.com is a good place to ask these type of questions and get really straight up answers, granted you have the basics to understand. also www.Computerhope.com is also a good place to get good info on this sort of thing.
Anyways i hope this helped a little at least