Can some explain the analogy of the Sun to the Good?

Projection of light is a powerful metaphor here. The brighter the source the clearer objects in reality appear. If you mistake shadows for objects, you may know the world in a way, but if you step back to see the puppet show and all the causal forces at work, it's no longer believeable. When you exit the cave and see the sun, it is as if you've perceived a pure Form. The lit earth are the true objects of nature. The cave fire is a mere imitation of the Sun's light. The shadows even more derivative. Reality descends ontologically from the Good in the same way.

For Plato, just as the Sun sustains or promotes life in the sensible realm or allows us to behold objects that are empirical in nature, so the Good is "the cause of all that is right and beautiful" in that it "produces and controls truth and intelligence, and he who is to act intelligently in public or in private must see it" (Republic, Book VII).

In short, the Good is the super-sensible principle of intelligibility. It allows us to perceive noetic objects of the intellect.

Without the sun life would perish and good is defined as that which furthers life rather than goes against it ...hope that helps

If we didn't have the sun, we would freeze and there would be total darkness

because sun provides stuff for us

so therefore its good?