In this dialog, you can specify a new relationship of the currently edited document. The currently edited document's name is initially pre-filled in the Left-side document field. The document that you want to make related to it can either be specified manually by typing its alias path into the Right-side document field, or by clicking the Select document button and choosing it from the content tree in the displayed dialog. The Switch sides button allows you to switch the left-side and right-side document.
The type of relationship can be chosen from the Relationship name drop-down list in the middle. You can only choose from a pre-defined set of relationship names, which can be pre-defined by your website administrators in Site Manager -> Development -> Relationship names.
Once you have the relationship specified, click the OK button to create it.