Please, give some next steps i'm complete lost where to start...
what to buy, how to program ?
Ouch. Without any clue about electricity or programming, the easiest, fastest and cheapest way to get the desired function is to buy a finished black box on ebay that does what you need.
If you don't believe me, fine go ahead. Start out with one of those: http://arduino.cc/en/Main/Hardware
plus a collection of resistors, a few leds and a few general purpose transistors and diodes.
Then go ahead an learn to program it a little. A good stating point is here: http://arduino.cc/en/Tutorial/HomePage
Once you have that down pat, you can think about starting to solve the problem above. If you fool around with the 24V supply too early, there's a good chance you're going to fry your microprocessor.
Korman