I am not much of a photo-taker, and know nothing about photo editing. But this newsletter, from Small Dog Electronics, has an article on photo editing in Apple's Photo App that I thought might be of some interest to you. Scroll down about halfway to get to the article. If interested, one can also subscribe to their newsletter, which contains interesting articles relating to Apple products, which, BTW, they sell. They are a very reputable dealer, and you can trust what they say, IMHO (In my humble opinion).
Jim Hamm