To shine is to give off a bright, glowing light. Your porch light shines at night, and if the sky is clear and cloudless, the moon will shine too.
The sun and a light bulb both shine, and things that simply reflect light can be said to shine too, like a diamond ring or clean, glossy hair. In a more figurative way, people shine when they stand out for doing something extremely well: "The lead actress really shines in her role as Lady Macbeth." The Old English root of shine is scinan, which means "shed light, be radiant, or illuminate," and also "be conspicuous."