Last year we pinioned our chicks. We used fingernail clippers, and did it when they were only two days old or so.
You clip of the last joint, so it is actually cutting off bone. It is the place that would be the 'thumb' on your hand. Let me see it I can find an example-
OK, you have the elbow joint, then the wrist joint, and on the wrist joint there is the hand bone and the thumb bone. the hand bone has the flight feathers on it, and the thumb joint is short and has (I think) the outermost three or so flight feathers. That is the one you clip.
Now they are grown and you cant tell by looking at them unless you spread the wings out. They cant fly, but we are not doing it again this year. I will just clip feathers if I need to. We had one almost bleed to death, we must have got too much bone. They all bled, and then they picked at each other. So it is up to you. If you do it get some stop bleed stuff.
See if you can find a diagram or something, that would make it easier to see what you are doing. You dont what to mess it up and kill them or maim them.