You raise the camera, frame, focus, and shoot. Two seconds max.
That's the challenge: you need quick thinking, a camera in hand, and a hair trigger. And, alas, there are many things beyond your control that will nevertheless prevent the picture from working.
I don't know how the classic street photographers managed to do it with cameras lacking autofocus and autoexposure, and film that had to be advanced to the next frame between shots. Of course, their misses weren't published. . . .
