Complex sentence: The 3D processing is done in two steps: the azimuth and range direction are focussed for the generation of 2D (azimuth-range) high resolution images and then the elevation focusing is done to get the third dimension which is the elevation direction.
Split into simpler sentences: The 3D processing is done in two steps: the azimuth and range direction are focussed for the generation of 2D (azimuth-range) high resolution images. This height information, along with the azimuth-range coordinates provided by 2-D SAR focusing, gives the third dimension which is the elevation direction.