Your feed shows posts from the topics you follow - in chronological order, with no algorithmic reordering.
From the topics overview:
From the feed sidebar: Topic suggestions appear in the feed sidebar. Click Follow there.
On first visit: When you open the feed for the first time, you are asked to pick topics you are interested in. Select at least one to start filling your feed.
Click Following on a topic page or in the feed to unfollow it. The button returns to Follow.
Follow topics that genuinely match your work or interests. Five to fifteen topics is a good starting point. You can adjust any time.
Under Discover, you will see topic suggestions based on your existing interests.