Yes you can nest functions in VBA.
The following example  controls the formatting of dates.
As you can see the Now function  (which returns the system date and
time) is used as the first argument  to the Format function, whose
second argument is the format picture.


Sub FunctionWithinFunction()
' Use Ctrl + G to display the Immediate window before
' running this procedure.

Debug.Print Format(Now, "dd-mmmm-YYYY")

End Sub