1. Why is it important that a List is a monad?
A. Its not particularly important. Its really just pointing out that monad is a very general abstraction - it wont tell you anything you don't already know about Lists.
On the other side, lists as kind of trivial examples of monads - they didnt really help me understand monads either.
Its like saying 1 is a real number - true, but it wont help you understand real numbers.
2. Why should i use monads?
A: I like to think of monads as things you can use in a for-comprehension (or the do notation in Haskell). If you can imagine writing something like
for {x <- thing; y<-thing} x + y
3. But a monad is just a monoid in the category of endofunctors?
A: There is deep category theory and math behind this stuff. It can be useful to talk about it, but when you are starting out its overkill. Don't worry about "getting" the really abstract crap at first, just skim right over. Programming in monads is a lot easier than the theory, and the theory can be learned after getting your hands dirty. Using monads is mostly just for-comprehensions.
ps:
"monoid" = there is a zero, and an add operation. like integers with +, or integers with *).
"functor" = thing that has a map() operation.
"endo" = self
"category" = kind of like a set. its a container.
So a monad has a "zero" or default monad, a way to add monads, and a map operation that returns another monad.
e.g List -> zero = Nil, add = append, map = the "normal" map with f applied to each element
Future -> zero = empty Future, add = do future2 after future1, map = make a future with the f applied to value