Make one big extrusion all the way to the center of the car starting at the edges shown in green. Make sure that the
x-coordinates of the vertices at the center of the car are set to zero.
A nice feature that was included in Max beginning in version 5 is the "Symmetry" modifier. This allows you to be able to see both halves of the car even though you model only on one side. Before version 5, you would have to mirror the geometry of the car as in instance so that any changes made to one side would be reflected on the other side. This worked fine but the problem was that there was always a seam down the middle of the car. With the Symmetry modifier, you can set it to weld vertices within a certain range thus allowing you to see the whole car without the annoying seam down the middle.
Select "Symmetry" from the modifier list shown by the red arrow. This adds a the Symmetry modifier to the top of the stack. Click the "+" to open the modifier and select "Mirror." This activates the mirror gizmo in the viewport. Move the gizmo in the X-direction and set it's X-coordinate to zero to make it lie at the center of the car. Now the car has it's other half with no seam down the middle. Make sure the mirror axis is set to Z.
You can also add a "MeshSmooth" modifier to the stack so that you can look at what the car looks like smoothed. Set the iterations to 2, which should be good enough for the purposes of this tutorial. You can set it to 3 for very close up shots of the car but generally smoothing to 2 iterations is usually enough. The picture shows what the car now looks like with both Symmetry and MeshSmooth modifiers. The front is starting to shape up but there is still some detailing left to do.
Make the cuts show in the green to add detail to the hood of the car. Adjust vertices as necessary to get a good shape.
Extrude the edges in green downwards as shown by the red arrows and then make the cuts shown in red. Adjust the vertices as necessary.
It's time to start moving towards the rear of the car. Select the edges shown in green and hold down shift and drag them to the edge of the door in the blueprint. Adjust vertices in all veiwports to shape the door.