To open this dialog box:
Go to the Work view.
Click the Add button and then click Link (URI).
Here are things you do in this dialog box:
means that resources of this category will be available in steps that use the Compare tool.
Below Resources for, select () one of these options:
URI means Uniform Resource Identifier.
See: https://en.wikipedia.org/wiki/Uniform_Resource_Identifier.
Your link can be also be a typical URL to a web site and so on.