50-50 is when both your trucks land on the curb and slide
some people aprroach the curb at an angle for this others like to go parralel to it
approach the obstacle at a comfortable speed ollie just high enough to get up the curb shoot your feet out at the curb at first don't worry weather the board comes with you work on aim.
if you land and slide to get off you can either ride off,kickturn off or ollie off
you might wanna try this still at first up to you
but remeber!! concentrate on the whole move the ollie in the 50-50 and the pivot out
this trick is a building block to many other grind tricks