The custom section allows you to show off content that you care about in its own section, using some sort of feed.
If you have videos in YouTube you'd like to show off, you can add them in their own section. Simply add a feed that looks like this: http://gdata.youtube.com/feeds/api/users/YOURYOUTUBEUSERNAME/uploads in the custom section.
If you would like to show off a specific category or tag, you can do that by getting the right feed. These are WordPress's instructions for finding those feeds.
You may also include external content if you like by providing a valid feed.
However, you may not include paid links out or link to sponsored/native content without speaking to us first. This is due to FTC regulations around disclosing paid content. Drop us a note at firstname.lastname@example.org to discuss how to do this.