If done correctly you will only need to clip a parakeets wings 1 time. This should be done by someone who really knows what they are doing. You wouldn't want to hurt your little tweety by accidentally clipping the shorter wings in their cartilage and joints.
You cut them when they grow out to be long enough to allow flight.
Birds have two sets of feathers.. primaries and secondaries. The primaries are the loooong ones along the edge, the secondaries are the shorter ones. Just cutting off the primaries is enough to disable their flight, while still being fairly safe to cut (very little risk of cutting a quick and having them bleed).
It seems cruel to clip a bird's wings. What are the benefits besides them not being able to fly away? If I ever adopt a birdie I don't think I will clip the wings. It just doesn't seem right. Am I just uneducated here?