In order to reference a record in CRM you need several key items, one of them is the GUID of the record. Depending on your browser settings it may not appear by default in the URL part of the form Window.
The easiest way to get it is to open a record and then hit F11 to display the form in a full-screen Window. Then locate the part of the URL (in red) that is between %257b and %257d (in blue). In the case of the campaign record displayed in the screen below the complete URL is as follows:
Note: Manually wrapped to fit better on the blog page
You will know that you have the correct text if the first set of characters contains 8 digits and the last set of characters contains 12 in this format: 8-4-4-4-12.