The parameter data area (PDA) is a special verision of the local data area (LDA), that is used in function, external subroutine, or helproutine objects. You can either define parameters inline like
DEFINE DATA
PARAMETER
1 #A(N2)
1 #B(N2)
1 #C(N2)
1 #D(N2)
1 #E(N2)
1 #F(N2)
LOCAL
your local variables
END-DEFINE
…
Alternatively you can also create a separate source object, similar to an external LDA.
DEFINE DATA
PARAMETER USING pda
LOCAL
your local variables
END-DEFINE
…
Note that you cannot use parameters with an internal subroutine.
I suggest you start reading the Natural documentation on Software AG's web site, especially the "First Steps" manual, if you've never worked with this powerful language before.