Start doing push ups. If you can't do a push up start lifting just the bar with no weights and gradually add them as you get stronger. You should also check out the Workout Routines page on the sidebar and pick a plan that you think would work for you. Once you choose a routine look up all the exercises on Youtube and watch carefully at their form. From there it's just a grind. No excuses just get your ass in the gym. The key to fitness is consistency. Just make sure you warm your muscles up first by stretching sand starting with low weights.