Don't try cork three, chances are if you can't rodeo yet a cork three will be more difficult.
Try a flat spin 3 first (or rodeo 3? i think your talking about a flat 3) but make sure you can do it on a tramp or something first so you know the rotation. After you get flat 3s rodeo's come very easy.
to do it, you have to run and plant with your left foot, then throw with your right arm and grab safety. or vice versa if you throw the other way. if you try and jump, then things get whack.