Chill on the marathon thing, and become a runner first. Develop an actual love of distance running. It will change the way you eat, think, sleep, and live your life.
Run 5Ks, 10Ks, and half-marathons. Learn what it's like to prepare for these races. Learn about nutrition and hydration. Develop a sense of appropriate pace and breathing rhythm. Find the best training shoes for the particular dynamics of your foot. (hint: don't shop for your next pair at Target, Kmart, or Foot Locker) Invest in the right running apparel. Find a training partner. Subscribe to Runner's World. And so forth...
Once you've transformed yourself into a person that loves to run on a daily basis, you'll then be ready to set your sights on the milage required for marathon training. This is not a sport for people seeking instant gratification. If that sounds like you, this will never work out.
Final comment — you are asking very good questions, so good luck!
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