Lots of good advice above....one thing to add: often new riders use too high a gear (one of the smaller cogs in back with the bigger chainring at the pedals) and therefore are required to push overly hard on the pedals-- which may not be good for knees, muscles, connective tissues, etc. Find a gear that seems fairly easy to "spin"....if its too easy you'll feel like a hummingbird going nowhere slowly. Bigger gears come later as you condition your legs. Besides, lighter gears spun a little more quickly can be aerobically effective.
Enough!! All the comments on getting a good fit on your inherited bike are well taken. Keep posting your progress or questions.....for good or ill, you're one of "Us" now.
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..... "I renewed my youth, to outward appearance, by mounting a bicycle for the first time." Mark Twain, Speeches
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