Ok is difficult to explain and this board do not allow uploading.
You have 3 points in an XYZ enviroment, that create a plane, lets call it 3-plane because it is made of 3 points. You can move any of the points at any place on XYZ and will still have a plane.
Now , you have 4 points on an XYZ enviroment, that can create a plane, lets call it quad plane because is made of 4 points. If you move any of the points in XYZ you will get a 3D surface. I indicated that it can create a plane because if the extra point is correctly aligned that will create a planar surface. That extra point can be moved on X or Y or Z to be aligned.
Then the info is XYZ values for 3 fixed points that already create a plane, and the value XYZ of the point that need to be aligned to the 3 fixed points to create a planar surface by change its X or Y or Z value.