Application Studio - url-open to pass a parameter from UD field

New to Application Studio. I have created a button and inserted the url-open component. Can someone guide me as to how we can pass a variable into the URL parameter from a UD field on the customer file.

I have managed to get this to work. A variable can be passed into the URL like e.g.
https://mycompany.software.com/CRM/Account/Index/{Customer.myvariable_ID_xref_c}