Step 1:

Highlight the group on the left that you want to add a resource to and press the "Add Resource" link.

Step 2:

By default you will be presented with a mini "word processor" with which to enter your text. Use headings to make your text more readable. To do this choose "Heading 2" from the drop down list on the top left. Bold is also useful for highlighting things and of course you can insert bullet points, links, images and the like.

Step 3:

If instead of direct entry you want to upload a file, just press the "Change" button. The word processor will disappear and you will be presented with a "browse" button that can be pressed to choose the file on your computer that you want to upload. This could a PDF file, a video or many other things. Make sure you type in a good description so your file can be located easily with search.