ok sorry i already know that but i need it in the 3-dimensional dash-wedge form. for instance how would you put your example into tetrahedral form?
The wedge and dash form represents a tetrahedron, the horizontal bonds are coming out at you and the verticle bonds going back into the page.
Try to draw zigzag forms of the molecules from both of their sides, so that the carbon skeleton is flat on the page and either the oxidril or the hydrogen comes out toward you while the other goes back away from you.
Other than that its just training. Invest some time to just look at and try to reconstruct and rotate the tetrahedron in your mind. There is no technique or trick to stereochemistry, it basicly boils down to being able to imagine 3d geometry.
If you take some time and are patient you will have no problems with these kinds of things.