In order to register at TruckersMP.com, you must first have your Steam profile made public, to pass the verification process.
The next step is to have at least 2 hours of play time on Steam for either Euro Truck Simulator 2 or American Truck Simulator.
Now we`re moving to the actual activation of the game, login at TruckersMP.com, go to My Profile - Settings then press on check now, http://prntscr.com/a1cl6l
The games should be activated on TruckersMP in 5-60 minutes and you`ll be able to login in game and play our multiplayer mod.