How will nearsightedness affect my lifestyle?

Only little changes. A person who becomes moderately or very nearsighted will have to remember to have glasses or contact lenses with him wherever he goes. If he forgets them, he can't see well enough to drive. He needs them for sports, to see a ball clearly. He needs them for swimming, to see in the water. At night, he needs them even more. Overall, glasses or contact lenses are only a minor inconvenience.
DMV caveat. In addition, please note that if your nearsightedness is severe enough, you may not pass the vision test at the dmv for a driver's license and would then be required to wear corrective lenses while you drive for your & everyone else's safety. This may be noted on your driver's license as well. It is best to get it checked out by an optometrist or ophthalmologist.
It should not. Nearsightedness should not affect your life, if you wear corrective lenses. Without correction, you will have difficulty seeing things at a distance clearly but if that is the only eye condition you have, it shouldn't significantly change your life. Once you get eyeglasses or contact lenses, you will be able to see more clearly.