What exactly do you not understand?
Because, you know, there are explanations in the
Damage Engine trigger (assuming you are talking about
Bribe's Damage Engine). Just look at the example map: there are two main triggers,
Damage Engine and
Damage Engine Config. Then look at the example trigger: there's one for editing the damage and one where you can use the damage for anything you want, like show a floating text above attacked units.