When you schedule many posts from your library to go off in certain dates and time, you have created a campaign. The content of the posts in a single campaign are selected from the RSS feed of the category you picked in your library when creating such campaign.
For example, when you create a campaign and pick the “Tips and Tricks” category as your source of content, the content in the “Tips and Tricks” category will be posted on the dates you have scheduled them to go off while creating the campaign.
Please, note that you must have added enough content to the relevant categories in your library before you can create a campaign using that category as the source of your campaign.