How do these traits of an elephant become chaned to adaptations?

Evolution is a process whereby random traits become settled and genetically inherited because they are, directly or indirectly, advantageous to the organism's ability to survive and reproduce. It is also possible for certain traits to become fixed via the process of random genetic drift even if they do not benefit via natural selection, so long as they are not actually disadvantageous to the organism. It all starts with small variations, and these become more and more pronounced over the generations.

In answer to your specific question, you need to look at the survival benefits to elephants of the five features you mention. The large ears of an African elephant (Indian elephants have smaller ears) assist with cooling - with such a large body, they would otherwise be at great risk of overheating. The tusks are used for uprooting trees, and are also of advantage to males in demonstrating their maturity and therefore their status as a potential mate. The trunk is a wonderfully adaptable and multi-purposed organ; it's not easy to be sure which of its current uses would have been the one which drove its selection process, but I would guess that its ability to grasp may have been paramount. The molars move forwards in the mouth throught life; if they didn't, the elephant's teeth would wear out from the grinding of its food, and the elephant would starve to death at quite a young age. And the feet - well, you can't imagine an elephant with small, dainty feet, can you? It had to evolve feet large enough to take its considerable weight.

For more detailed information on evolution and the process of adaptation, see http://en.wikipedia.org/wiki/Evolution and http://en.wikipedia.org/wiki/Adaptation. You will also find http://en.wikipedia.org/wiki/Elephant#Physical_cha... of interest.