The heavy, thick, 6 – 10 feathers from the tip of the wing to the first joint back, are considered “primaries”, and best for grinding, cutting, chopping, or burning to your preferred shape.
From that joint inwards are considered “secondaries”, which are best left for flu-flus. Been my experience they are to thin and flexible to bother with shaping, although they do make for cool crafts and ornaments.
Right wing comes from the right wing and left wing from the left…8^) Kidding aside, although you can jig up the left wing secondaries by clamping them in a right helical clamp and they will work fine for flu-flus.
Also, if the secondary feather is big enough you can use both sides of the quill for flu-flus... Just my 2 cents.