The focal point is the part of the painting that catches your eye first. The focal point is sometimes called the “center of interest.”
The focal point is sometimes in the middle of the painting, but not always. Look at the painting The Wedding Feast by Pieter Brueghel. Your eye probably goes over to the right, to look at the person in the blue shirt with the tray of pies. Why is this?
Color is one reason. The bright blue shirt and white apron (and the two white pies) really stand out against the dark, reddish colors of the rest of the painting. Perspective is another reason. Most of the action takes place along a diagonal line, and the person in the blue shirt is at the end of the diagonal that is closest to you.
What if the person in blue were wearing a black shirt and a brown apron instead? Then what would be the focal point? Your eye might go to the person in the red shirt holding the other side of the pie tray. Or it might go just to the pies themselves.