Teeth in toothpaste commercials are gleaming. They sparkle when the light hits. When you see this word, think of a bright reflected ray of light, on teeth, on water, or in someone's smiling eyes.
A new skyscraper that reflects light might also be described as gleaming. If you are excited to move to a new place, someone might say that your eyes are gleaming with excitement, especially as you view the gleaming wood floors and gleaming freshly-washed windows of your new home. The word has a clean, glittering, sparkly feel to it.