Upvote means you find the content helpful, interesting, amusing, or just want to thank the person who posted it. It's your way of saying you like it and want to see more content like it! Your upvotes will push interesting content to the top of the page, so more people see it! The thumbs down button is for downvoting. It means you think the content detracts from Glow Community because it's offensive or irrelevant. If a post receives enough downvotes, it will get dropped in rankings, meaning fewer people will see it. If you think a post should be removed from the Glow Community, you should report it to the admins. But downvoting it also helps too, because it means fewer people will see it in the meantime.
The purpose of this feature is to help you quickly surface interesting, helpful content, while simultaneously burying objectionable, offensive content. It's your Community, your call!