Then let's keep this simple.
Is this an MS Access question or a FileMaker question?
Because I really don't know what a "summary count field" or a "Portal" is without any context.
In Access if you have a Table/query named: "Orders", and you want to sum up all the "Quantity" Fields of all the records that are (filtered on) a Country of "USA", then you would use something like this:
YourValue=Dsum("Quantity","Orders","Country=" & "'" & USA & "'")
If the Filter value is numeric (say the employee Number), then the syntax becomes:
YourValue=Dsum("Quantity","Orders","EmployeeID=" & 3)
There are various variations on this depending if these are hardcoded values or variables, but I am sure you get the idea.
In Access see the help files on DSum (aggregate functions)
;-)
JeffCoachman