They are dead simple, they fit them to service rifles.
Position the rear-sight so you can see the foresight blade clearly/sharply through the aperture. This will usually be very close to your eye, like with a scope.
For bell-target I suppose you would use a square-post fore-sight element, placing the square top under the black bit of the round target. Maybe a ring-element would work better with bell-target, I don't know what size the aiming point is, get a ring that is not too big or too small, you need a good ring of light around the black aiming mark.
You look through the sight, kind of ignoring the aperture (you don't consciously try to line it up) and by some kind of miracle your eye/brain automatically centres the foresight in the middle of the sight picture. Ignore the foresight hood, that is just there to protect or support the blade. You just see the foresight blade in the centre of your field of view. If you do 'look' at the aperture it will be all blurry and probably not look circular. So don't!
Place the post under your aim-point, get your breathing sorted, and press the trigger.
Its actually the easiest sighting system to use.