Has anyone actually completed a rubix cube..

It is very easy to solve the rubik's cube once you know the standard moves to solve the puzzle. Though there are books giving the way to solve the puzzle, why don't you try it yourself with the little help I give. Solving one side is easy. But make sure that while one surface is of one colour its rim is also not a jumble of colours but four colours on four sides. Then experiment and see what moves you can make without upsetting what you have done. For instance if you hold the made surface upwards and make a movement like down, right, up, left the top surface will be upset. If you reverse this with right, down, left, up then it will be back in the same way. Why not do this but make a small change before the reverse movement. Then see what happens. This will help you to solve the cube on your own.

Those things are so hard it's crazy, I mean you have to be a genius to finish one of those.

no. but was able to do some tricks when it was complete. like changing the design on it. that is a hard thing to complete, or I should say it takes a long time. have a good day.