Welcome to ReScript!
The most up to date resource are the ReScript docs: https://rescript-lang.org/
There is a somewhat recent book: Introducing ReScript: Functional Programming for Web Applications | SpringerLink
The content is already a bit outdated though. Most notably there is no async/await, it is using the old standard libraries which are in the process of getting superseded by ReScript Core and it utilizes auto-currying a bit, which is not the default behaviour since ReScript 11.
And here is a collection of resources that I update every once in a while: GitHub - fhammerschmidt/awesome-rescript: A collection of materials about the ReScript programming language and toolchain.
I also want to highlight a more recent video course by @Exegetech here:
Last, but not least: use this forums search function (or just google) and if you don’t find an answer don’t hesitate to start a new forum thread and ask a question!