Yes / No parameter in SSRS

I am very new to SQL / SSRS.

I am creating a report in Visual Studio and am trying to create a parameter with Yes / No Values -  when "Yes" is selected, it will show all dates from the "Valid_Until" field that are greater than now and when "No" is selected, it will show all dates. I have tried several different things with various scripting errors.  

My parameter has available values

Yes

>=Now()

No

>=Now()-20000

(When I specified a date, I would get an error (An error has occurred during report processing (rsProcessingAborted))

In my dataset, my query is straightforward:

SELECT        FreightInfo$.*
FROM            FreightInfo$

My question is that I can't understand how to connect the parameter to the correct field.  Parameters can't have references to fields, so how do I express that I want the "Valid_Until" field to use the parameters that I set.  I'm sure there's an easier way to construct this, but don't have the experience to understand what needs to be done.

Thank You in advance!