How do you jump on to a metal bar on a skateboard?

It's called grinding. It takes alot of practice, the basic grinds are 50-50, boardslide, 5.0, Smith. You have to Ollie onto it and move your board depending on the desired trick, it takes some people years! Some more advanced are Overcrooked, Lipslide, darkslide and Nosegrinds!

Hope I helped :)