how does that work

nobody knos

?????????????WTF?????

There are two (main) ways IM can work.

Centralised
http://en.wikipedia.org/wiki/Centralized_system

and

Decentralised
http://en.wikipedia.org/wiki/Decentralized_system

Then once you have decided on the system you will use you must create a protocol:
http://en.wikipedia.org/wiki/Protocol_%28computing%29

Of course, you should hopefully use encryption:
http://en.wikipedia.org/wiki/Encryption

Then you will need a client, probably with a GUI:
http://en.wikipedia.org/wiki/Client_%28computing%29
http://en.wikipedia.org/wiki/GUI

If you choose a centralised system you will also need a server:
http://en.wikipedia.org/wiki/Communications_server


Any clearer?

Ta,

~C