Three things help me when horror happens.
First, look for the heroes, because every terrible story or tragedy has a hero, someone who shines virtue (courage, charity, sacrifice, mercy) into the dark place.
Second, combat the darkness and the helplessness by doing important work: love the person right in front of you, right now. Don't despair about all the evil people we cannot control, or spend too much time in the vortex of news and debate. Focus on the face closest to you, see its dignity, and love it. Do that every day. (Love God. Love others.)
Third, John 1:5: the light shines in the darkness, and the darkness has not overcome it.
And it never will.