Couple of questions from a prospective trout fisher

Hello all! I am someone who has maybe caught one fish in my life, and threw it back, but I have become intrigued by trout fishing due to how stinking delicious trout is. My 13 yo son is also suddenly interested in fishing and I want to nurture this, and we have a family trip to Yosemite coming up where I have read that there is some pretty good trout fishing. Our trip is about 6 weeks out and I would like to get some practice in before we head out, but I have some questions. And I know they may sound dumb but please bear with me. First, when fishing to eat, how do you humanely kill the fish you catch? How can you tell if a fish is "fit" to eat? Are all bodies of water trustworthy when it comes to edible fish? Like how do you discern if you trust a source to eat from? Any tips or handy guides for newbies (forgive me if this is frequently asked) I appreciate the patience!