FSXA choose the right file

In the tutorial Arno talks about choosing the right file. He has already done so. What are we supposed to choose? the tutorial does not say. Above it says to NOT choose the _o.asm file. FINE... so what DO we choose?

Next This is compiled to an asm file. Fine..... but does this asm file work in a library which takes mdl files and makes a bgl out of them? I know we an rename as we wish but the above questions remain!