On the far left is the information about your research library.
You can create groups to collaborate and share research (citations, PDFs, and notes).
This pane displays the contents of the folder you have selected on in the left hand pane.
For example, if you have highlighted All Documents, a list of all the documents you have in All Documents will appear in the middle pane. The information includes all of the relevant citation information to help identify the document.
On the far right, the pane displays the document you have highlighted (click on) from the middle pane. The default view is Detailed; there are also options for Notes and Content (upper right).
You can add any notes or quotes from the document.