Well, the physical action of pulling them from the ground is pretty easy. Though actually, there are often very delicate parts of the mushroom just at ground level, or below ground level, so careless picking can leave behind parts of the mushroom that are crucial to identification. So even the physical action of gathering the mushroom is something that needs to be done correctly!
Then there's the matter of spotting them. This takes practice, also. Experienced mushroom-hunters will detect the presence of fungi where novices will not. Mostly this is a matter of patience, though.
And then there's the matter of identifying them. At sight, even a professional mycologist can usually only identify about 80% of what they find (on a good walk), because there are just so many things out there! (see Question 2) Given a week with a professional library and a microscope, that number would probably go up to 97% or so; and that's a professional. So if your interest is in knowing the name of EVERYTHING you see, your learning curve will be steep.
However, if your interest is in finding nice-tasting ediblemushrooms, you're in luck, as there are fairly common edibles that can be learned quickly (as can their poisonous look-alikes). In fact, the most common mushrooms in a given area account for over half of the mushrooms that you will see, so once you learn those, you have accounted for the majority of what you find.
And it's fairly easy to acquire a sort of standard level of knowledge in any given area. For example: once you can recognize a Russula (a common genus of mushroom), you can recognize a "red-capped Russula". Once you can do this, you are on a par with 99% of the non-professionals in the country. Then, there are a couple of red-capped Russulas with distinctive features that make them easy to identify: for example, Russula rugosiceps has lots of little wrinkles in the surface of the cap, as if it was paper that someone let get wet and they dry; and there are groups of Russulas that have such features, for instance there are three Russulas headed by Russula rubescens that stain grey or black on the stem. Once you know these sorts of things, you are on a par with all but 3 or 4 professional mycologists in the country. Then there's the level of knowledge that would enable you to distinguish those three red-capped Russulas that stain grey, but the only people who know that are the professional specialists in Russula (Russulologists?), and no one has a specialist's level of knowledge in all the major groups of fungi.
To sum up, no one, anywhere, knows EVERYTHING about fungi. But it's not that difficult to get acquire a general, basic level of knowledge about the field. This web site is a good place to start!
