It's easy! You can attach documents, images, or links to your agenda using the Attachments section.
In an existing agenda that already has an Attachments section, simply click the message 'This section doesn't have any items yet, click here to add one!', choose your attachment type, give it a title, and then either select a file to attach or paste in a URL. When you click save, your document, image or link will be attached to the agenda. Everyone who has access to the agenda will be able to click on it and see the document, image or URL. You can add as many as you want.
If your current agenda doesn't have an Attachments section you can click on 'Edit Sections' underneath your agenda title at the top of the page. Then you can click 'Add Another Section', select the 'Attachments' section type, save and then follow the process above.