thevenin theorem and norton theorem

[stupif]

can someone tells me what is purpose of using thevenin"s and norton"s theorem??
and what these theorems contribute to electrical engineering's field?

thank you

[MATLABdude]

What's the purpose of a ball-peen or framing or sledge hammer? They're all used to hit things with, but are better at particular jobs. So it is with Thevenin's and Norton's: they're both used for circuit analysis, but can greatly simplify certain jobs, and allow you to abstract entire portions of simple circuits, reducing them down to a simple voltage or current source and a resistor.

The whole concept of black boxes and abstraction makes EE's lives easier.