A focal point (or center of interest) is the part of an artwork you look at first. Artists focus your attention on the focal point by using various art elements and principles.
What do you see first? In his painting, Summer, Henri Rousseau draws your eye to the figures by painting them with bright, saturated, complementary colors. The horse and the woman's scarf jump out because of the high contrast of white against the darker background. It is also common to place the focal point in the center. In this case, the focal point is framed by the lines of the tree branches.