Find the vector equation of a plane through the points A(2,3,-1) , B(-1,2,4) and C(-4,1,5). Draw in the vectors [math]\vec{OA}[/math], [math]\vec{AB}[/math] and [math]\vec{AC}[/math] first. Next try to use the tool for drawing planes with three points. You will usually get the Cartesian form of the plane.
Adjust the points A,B and C if you have another set of points given.