You probably don't speak latin, so this title doesn't mean much to you yet. It can be roughly translated as "Why did God become a human being?"
This phrase was used by Anselm as a book title in his explanation of why God would want to become human. It was revolutionary in it's day! And I think this idea is still rather revolutionary. Is God human? Indeed, that is the claim of Christianity, at least in part. God took on our very nature when his son became incarnated in flesh. That's when the controversy started. How do you explain that one? While theologians proposed many different formulations, the Church did settle upon on an official formulation at the Council of Chalcedon in 451. What they came up with was complicated. (and personally, I don't find it all that helpful).
Somethings in life are better left as a mystery, something to ponder and wonder. I don't have to understand how a sunset works to appreciate its beauty. I don't have to understand the chemistry of love, to love my wife or my kids. Maybe someday I will understand it. But I don't have to understand it to appreciate its significance.
It means that by becoming human, God solved the problem of sin. It's been taken care of. You don't need to worry about any more. Because God became human now there is a way out of our predicament. When we are joined together with Christ Jesus, we become a part of his story from then on. His story becomes our story, forever. His destiny becomes our destiny, forever.