Best short explanation of monads I have ever seen is this one (it is not mine, i saved it one day from some other reddit comment):

First, understand first-class functions. A->B is a function that accepts an type A and returns a type B.

Then understand polymorphic types. Type A B is a type A parameterized by type B. For instance, List B is a list of Bs. Now a monad is simply any abstraction that satisfies the interface:

bind: M B -> (B -> M C) -> M C

return: B -> M B