Context: after eating a death cap (Amanita phalloides), you'd notice a few of the symptoms at first, but these usually resolve after a day or two. After this, you'll enter a latent phase where you feel fine, but your liver and kidneys slowly start to fail. By the time you notice, it's usually already too late.
If wish to learn how to forage for mushrooms, join a local mycology club and go out with them. They can identify mushrooms for you and teach you how to do so yourself. They can also recommend good local field guides, I see a few folks in this thread recommending All that the rain promises and More which is a reputable guide but it's also spectacularly out of date and only applicable to Western North America.
It's important to know what you're doing but mushroom identification is not nearly as difficult as some of the comments here make it out to be. There are far fewer deadly mushrooms out there than most people think and it's fairly easy to familiarize yourself with all the deadly species in your area so you can avoid them.