Within Broadcast, the Content tab (sometimes called the Content Hub) is where all of your drafted, planned, and published Stories and Events are created and listed for Team Members. Content that is published and approved is shared with Subscribers via several select channels, including News Digests, Broadcast Mobile, Blast Content Block, the Content Archive, and Teams & Slack.
Below are resources that go more in-depth about the options available under Content.
Creating Content
Content Hub
Content Controls
Channels