You would use the LIKE operator and put an asterisk on each end of the arguement in the query criteria. If you're using the design view, turn on Totals and set the Total row to "Where" (The Show checkmark will turn off.) In the criteria row type:
LIKE * & (form reference here) & *
Access will put in the quotes where needed for you. Since this is a non-show field, you'll need to drag over the same field to another spot. Just delete out the "Group By" that it automatically sets the Totals to. Hope this helps.