On the docket on Monday at a Minneapolis courthouse is the biggest police brutality case in the United States in three decades: the trial of Derek Chauvin, a white former police officer accused of killing George Floyd, a Black man, last year. The case centers on a 10-minute video, shot by a bystander, showing Mr. Chauvin kneeling on Mr. Floyd’s neck. That video reverberated around the world. We look at the contours of the trial and what we know about it so far.