There are 2 approaches to Par Designer:
1.) copy and open an existing par-file, that is similar to the one you want to create. Then you can simply go to the aeroplane tab (2nd one) and change the values (explanations of the values is in the right column)
or
2.) create a new par-file from scratch, then you can use the first tab to do some basic calculations. The outcome of that calculations is taken over to the aeroplane tab and can be seen as a rough proposal to what you will have in the end.
I personally use method 1, because in most cases there does already exist a plane with (in a wide sens) similar behavior. And then I start modifing. Somtimes the modifications are that big, that in the end it has nothing to do with the original file i took...
