Take a fork strap it to your closed fist and jam it in an electrical outlet, that lethal enough for ya axl?
What more help do you want? There have been several links that provide plenty of usable information on coil guns and their designs, and a simple Google search will find you more, the onus is on you to teach yourself electronics we can't hold your hand and it's not possible to teach a course through a forum, you need either one on one time with a tutor or to follow some other introductory electronics courses, which again there are plenty of if you look on Google.
You seem to just want answers and a working product in your hands like magic, not gonna happen, that coilgun you linked from Youtube was very well put together, and probably cost the guy that built it a couple hundred dollars of material and many hours in fabrication and testing, and he obviously knew exactly what he was doing. Also you'll notice how close range all those shots are, it has no distance and no practical power, it's basically nothing more than a very controlled thrown rock, all the stuff that it broke was hard materials and the shot was a blunt point. If you wanted any kind of range you'd have to use a very tiny shot and the total delivered power would drop VERY quickly with the increased range. You can buy for probably less than the total cost in both time and materials, a hand pumped BB gun that will deliver 10 times more energy, and that's at distance, a paintball gun would work better.
All you see is a neat gimmicky little toy and you want it and you want to build it yourself, you have no clue how to go about it, so aside from what links have been provided so far you're not going to get anymore help here.