Explv's Script Tutorial will explains most commonly used API methods for scripts. Explains how to setup Intellij for scripts, if you are using Intellij.
You could learn enough Java to make basic scripts from Code Academy Learn Java course. Just google Code Academy and sign up then find and add the java course.
This could probably teach you a few things over time as well.
Beyond doing all this it's kinda useless if you don't try and utilize what you are trying to learn to get a feeling for it.