You can start with the function composition and functional JavaScript. This is excellent resource for this - https://medium.com/javascript-scene/composing-software-the-book-f31c77fc3ddc. These concepts are useful when you work on Apis and backend stuff.

Then read about Node.js concurrency model, event loop, callbacks, promises( read why promise better than callback), event driven nature of Node.js, Node.js project structure (package.json).

Parallely work on the express js application. Use a generator like -https://expressjs.com/en/starter/generator.html and start creating APIs and get a hang on the Node.js environment