My personal alternative take to the usual monad tutorial — greatly simplified:
"Functor", "Applicative", and "Monad" are all just generalizations of the concept of `map` and `flatMap`.
1. Something is a "Functor" if you know how to call `map` on it, nothing more. "I can take a box of things and turn it into a box of other things, 1-to-1". On lists, for example, this is just `map` itself
2. Something is an "Applicative" if you know how to call `map` on it, but also know how to take a non-boxed value and put it in a box, and also know how to combine boxes in order
3. Something is a "Monad" if you know how to do all of the above, but also know how to call `flatMap` on it, nothing more. "I can take a box of things, turn each thing into a new box, and then combine them all in order". On lists, for example this is just `concatMap`
There's nothing really more complex to it, besides how you squint at various things (like functions) to fit them into the concept of `map` and `flatMap`.To answer your questions more directly:
1. Monads themselves are neither necessary nor sufficient to perform side effects in Haskell; they don't directly enable the effects, but they *do* help place guardrails on the actual unsafe, low-level code which *can* perform the effects, safely and in an ergonomic and composable way
2. Yes, "Monad" is just a name for a recurring way to approach a problem. Like in most math and programming, a certain repeating pattern was noticed, and given a name. Because of the math origin of the term, you get "Monad" instead of "flat-mappable"
3. Like any other tool, you reach for a monad when you have a monad-shaped problem. They're just one (powerful) tool for solving certain problems
