Download whichever you need and print it. There is a regular, and a wide-mouth version available.
After printing, put some bait in a canning jar and screw the lid on. This bait can be pieces of fruit, fruit juice, or anything else that will attract fruit flies. As luck would have it, I haven't had any fruit flies around since I finished this (not that I'm complaining), so I haven't had a chance to test it, but I've had good luck with cruder traps of similar design in the past. Apparently a mix of some fruit juice with just a little bit of vinegar in it is a decent bait.
Place the baited trap near where you have fruit flies. They should enter through the hole at the end of the inverted cone, and will be unable to escape.