I enjoy finding mushrooms and trying to identify them. I use several good books on Mycology. The description in the book, apart from good photographs of the fruiting body, should give you a thorough description, pointers on where you are likely to find it and fruiting times (time of year). Fungi are usualy described as edible, non edible, poisonous or deadly.The non edible and deadly varieties are self explicit, they'll either kill you or taste so bad that you won't want to eat them. On the other hand, MBSL, you mention Parasol mushrooms (Lepiota), although normaly classed as edible, they can cause digestive disorders in some people, so in some books they are classed as mildly poisonous.Lepiota Procera should be safe to eat, but are you sure it's not one of it's close relatives. Also some fungi react unfavourably with alchohol and other common drugs.There are very few 'deadly' fungi, most inedible ones will either just taste awful or make you sick.
Tawney Grisette should be OK for most people to eat but looks very like Amanita inaurata, both are very common and both Autumn fruiting, the difference being that the latter will probably make you ill.
The rule is unless you're 110% sure, don't eat it. Even the experts sometimes get it wrong!