First, be aware that creating piles of photos for stock sites can require a lot of hard work—for an uncertain, and perhaps tiny, reward. If your pictures don't find buyers, you simply won't make money, no matter how much time you spend on them. You may also have to invest in expensive gear, like a quality camera, lenses, lights, or tripods, to get your work up to the required standard. So don't treat this as a full time job or a get-rich-quick scheme, because you don't have any guarantee that you'll make enough money to support yourself. In the end, you should be practicing a hobby you enjoy and having fun, with the money as a secondary concern.