Running 26.2 miles is a long way. It is very demanding on your muscles, tendons, ligaments, bones, cardiovascular fitness, and is just as demanding on your mental stamina. At any one time, 50% of all runners are injured. They have shin splints, plantar fasciitis, stress fractures and unexplained niggles.
Do see your doctor for a check-up before engaging in any strenuous activity. If you experience any soreness other than general fatigue, you must see a professional right away for a quick fix.
Running is addictive. Once you finish your marathon, you will not be the same person you were when you started training. You will be stronger in your body and in your mind. You will know that sense of freedom unique to runners. You will salute others in your neighborhood with that grin known to all runners. And you will become a better person.
If you have the guts to commit to a marathon, you should start by familiarizing yourself with running terminology.