Car 3
Select the door Surface to convert it to a Mesh.
Select a vertice near the corner and Delete it. Place the cursor as in the picture.
My method to model is: i made the basic shape with Surfaces, convert them to Mesh and then add details.
Add-Mesh-Circle. Shape it like the image. In side view rotate the circle and grab the vertices to fit the guidelines.
It's time to close the hole. Select 3 or 4 points, then do Shift-F to make a face. There are better ways than others to build faces. Do some tries.
Select all the vertices of the circle. In Side view, Extrude, and Move the points to the side and scale down a bit. Repeat the procedure and then build faces to close the hole.
After the conversion you must press the Set Smooth button to smooth the object, but as you can see in the first image above, the result is not very good. Use Auto Smooth instead. Press the Auto Smooth button, set "Degr:" ( try different values), Tab key to out Edit mode and press "Set Smooth" button (you only see the result after the scene rendering).
Select the last row of vertices. Copy and move them slightly to the right. Extrude, Move to the right and repeat!
When you move, rotate or scale, you can limitate the movement to one direction; with a 3 mouse button (with a 2 button press Alt-left click) move the object in the desired direction then press middle button... and the object it'll be on a "rail".
Select the 3 rows that surrounds the circle, Copy, Move to the right and align with the background image. Grab the points to fit the rear door and build faces with the previous extrusions.