It mean portions. So 1 part could be 1 cup and then two parts would be 2 cups and 1/2 part would be 1/2 cup. But you can change these portions to fit your need. It’s basically a less specific term so people can choose the amounts that are most useful to them.
I’m confused what you mean about using half gf baking mix with half whole grain gf flour. Is the whole grain gf flour recipe on your blog? Is it the second flour mix listed?
Hi! Sorry to confuse you, I think this second mix was also listed in this issue of Delicious Living, but wasn’t necessary for the apple pie recipe so I didn’t think to post it. However, if you are just substituting for non-gluten free recipes I’ve heard what works is to use a general purpose mix (like bob red mills) or the one listed here and then add 1tsp of xanthan gum for every cup that you are substituting in. So 1 cup of gf all purpose mix and 1tsp of xanthan gum equals 1 cup of regular flour. This is of course a general rule and so will not work perfectly every time. Hope this helps!
Gluten Free, Soy Free, Vegan 
what does parts mean?
It mean portions. So 1 part could be 1 cup and then two parts would be 2 cups and 1/2 part would be 1/2 cup. But you can change these portions to fit your need. It’s basically a less specific term so people can choose the amounts that are most useful to them.
I’m confused what you mean about using half gf baking mix with half whole grain gf flour. Is the whole grain gf flour recipe on your blog? Is it the second flour mix listed?
Hi! Sorry to confuse you, I think this second mix was also listed in this issue of Delicious Living, but wasn’t necessary for the apple pie recipe so I didn’t think to post it. However, if you are just substituting for non-gluten free recipes I’ve heard what works is to use a general purpose mix (like bob red mills) or the one listed here and then add 1tsp of xanthan gum for every cup that you are substituting in. So 1 cup of gf all purpose mix and 1tsp of xanthan gum equals 1 cup of regular flour. This is of course a general rule and so will not work perfectly every time. Hope this helps!