Thank you very much, John. This was just the information I came looking for.

I would like to add for others who need this information that I had to
remove extra [] via SQL view after I added the parameter via the design view
(kept getting an error about exta []).

Cheers,
Birgit

Open the Query in SQL view and put

PARAMETERS [forms]![frmCuffsShippedMain]![txtStartDate] DateTime,
[forms]![frmCuffsShippedMain]![txtEndDate] DateTime;

at the very top of the query, before the SELECT statement; or, equivalently,
right click the background of the tables window in query design view, select
Parameters, and put the parameters (exactly, they must match byte for byte) in
the left column and choose Date/Time from the dropdown in the right.