Once you have created a new Module, or you decided to use an existing Module, to add content start by going to the Content tab and clicking "Add and Arrange Content".
After clicking the "Add and Arrange Content" button, you will be taken to the Arrange screen.
Here, click the "+ Insert" button to add content.
You can choose to import content from your computer, Box or DropBox, or insert a YouTube video. In addition to uploading existing content, you can also add a Quiz or Survey. Select your desired content type to add to your Module.