Across the top is a bar that will take you to some of the more popular subreddits: politics, pics, funny, etc. On reddit anyone can create a subreddit, here we would probably just use some preset categories. The default front page draws from some set of the subreddits (here it would probably be all of them, but users could go to the subreddit pages to see only posts in that category. users on reddit can subscribe and unsubscribe to subreddits, to determine what reddits are eligible to show on their individual front pages. A logged in user might go to reddit and only see posts from the science, technology, and programming subreddits.