Only one wing should be clipped, as this will unbalance the bird. Clip both and it can still fly. Chickens moult and grow new feathers, so you will need to clip their wings at least once a year.
The small, pale feathers under Dudley’s thumb are called ‘axials.’ You should cut the larger, paler secondary flight feathers immediately in front of them. A good pair of large, sharp scissors will be needed.
Here Dudley isolates the feathers he will clip.
Pull the wing outward so the feathers are splayed then begin to cut directly below the axials.
This won’t hurt the bird.
You don’t need to clip all the outer wing feathers. This is as far as you should go.
Note the small brown ‘covert’ feather (so called because it’s hidden), which Dudley has left in place. This shows you where you should stop cutting. The bird is now no longer able to fly.