How might I create a license key?

Hello.

Can I please enquire.

I'm looking to build a simple program which would register and generate a license key and add/edit/delete and look it up on a online database.

In the same any other companies register their software their software (eg Microsoft etc)

Dose anyone know how to do this, or know of any code which would work?
Also how do I get a programe to communicate with a website? - I've lost my notes on how to do it.

If anyone could write a simple program for me to study - that would be a help.

Thank You.