How do you do a project about the sun?

Not sure what your level is; this may not be appropriate. You can make a pin-hole projector and actually project an image of the sun onto a piece of cardboard. If you do it right, you can get an image that is large enough so that sunspots may even be visible! You could also have classmates do an actual estimate of the diameter of the sun (or you could explain how you did it with your projector). If you carefully measure the distance between the pinhole and the surface you project the sun's image onto, and then carefully measure the diameter of the image right at that distance, you can do something interesting. The proportion of the 2 lengths is the same, no matter how big the distance gets. Can you see how you would "measure" the diameter of the sun this way? By the way, never, never, never look directly into the sun.