Mindfulness is a curious observance of the events as they unfold, being part of them and being above them at the same time. You start paying more attention and notice satisfying and beautiful things that could bring you joy.
You learn to find joy in small things, being grateful and appreciative, lowering your entitlement attitude and letting go of disappointment resulting from it, when your expectations were not met.
Mindfulness is many things, which you will keep discovering throughout all Mindfulness courses. But also after you finish them and continue your practice on your own. Probably, the best way to describe mindfulness is the ability to live your life instead of carrying it.