Bound form scenario: Use the On Current event of the form. populate the label.caption
UnBound form scenario: label.caption = dlookup(..,..,..) or use a recordset.
Since I remember how hard it was for me to get my arms around the DLookup syntax (even looking at the help file) I will try to help by being more explicit:
If your query already returns a single value then you don't need the criteria part of the DLookup, so it will be modified to look like this: