>>1513732"Field Guide," type series of books are a good place to start. Pick one book, for your location area like one for plants, take only it out on the trail. Read it and start identifying. Ones for plants will be more instant gratification since there's a shit ton of plants everywhere. Ones for animals and fungi are more rewarding since animals are usually shy and fungi are a rare find. Once you can identify things correctly, you can move onto either their uses for you or their place in the ecosystem. These two things can be more difficult since there's usually not a single book or resource that can list everything properly for either. Expect to go online a great deal for the bulk of that information. The best way to learn uses is to actually harvest and use them at least ten times. The best way to retain this information is to teach someone else, after you've learned it well enough.
