I started by going through the Java tutorial[1] to get a feel for it. It's fairly approachable and you don't actually need any Java knowledge.
Once you familiarize yourself with the concept of rules and targets, you can follow the instructions for whichever ruleset you want to use. The official one for JS is rules_nodejs[2]
Another thing that really helped me cement my understanding of Bazel was to deep dive into Starlark and write my own rules. The examples repo[3] is a great resource for that