Any simple guide for explaining how to implement a `future` for async/await?

Hello people,

I'm trying to learn async/await by implementing my own minimalistic Future (Ha!), my main source is the Async book chapter 2.

HOWEVER (annoyingly), I've hit some blocks, mainly from the part that involving futures crate, because not every line of code of the crate is explained.

So I want to ask is there any tutorial/book that can help me to understand std::future::Future and async/await work without having to dig into futures crate first?

Thank you!