Need ideas on using $Expression/$Multiline expression on USD Navigate to URL action call

Hi,

I'm a newbie with regards to using $Expression for creating a URL : https://msdn.microsoft.com/en-us/library/dn864934.aspx 

Here's my scenario:

• I have loaded a new CRM form within USD and would like to populate the values of the custom fields of the form. (e.g. Firstname, Lastname, Address1) using the URL that I'll be composing using the $Expression.
• I prefer it to be dynamic the form will be opened inside a Contact session.

It would be helpful if anyone can provide some samples?

Big Thanks! :)