We start by introducing monads simply, in a way functional programmers can understand. We use the maybe monad as an example. We describe Kleisli categories, monoids in monoidal categories and why a monads is a monoid in the category of endofunctors. We describe how monads relate to adjunctions, algebras and the Eilenberg Moore category. We also describe action monads, probability monads, and a connection between graphs, categories and monads. For more about probability monads check out Section 2.1 of https://arxiv.org/abs/2006.01631
More about the connection between categories and graphs can be found in http://eugeniacheng.com/wp-content/uploads/2017/02/cheng-lauda-guidebook.pdf
Also, see my previous video
https://www.youtube.com/watch?v=CYuG-wYx77o&list=PLCTMeyjMKRkoS699U0OJ3ymr3r01sI08l&index=24
for more background on monoidal categories