When a topic is featured, you can see that topic in the main home feed, so more users will see and follow that topic. Only admins can feature a topic. Follow these simple steps to feature a topic:
1- Click on the All Topics, on the left toolbar, to go to the topics page:
2- Click on and open the topic you want to be featured (in this case I chose the topic Bot User):
3- Once you are in the page of the desired topic, click on the star sign to feature the topic.
4- Now you can see the topic in the main home feed when your refresh the page.