API's
Welcome, to make use of these API's you must know how to program and have minimal knowledge of the Java or Kotlin language, and have some experience in developing plugins for SpigotMC, in addition, you must know how to use the IDE of your choice, likewise, the documentation will guide you in the implementation of the API in your plugin.
API Integration
To integrate the API to your project you will have to include it together with the compilation of your plugin. This process will depend on the IDE you are using, for IntelliJ IDEA, you should go to: File > Project Structure > Project Settings > Artifacts, you will have to create a new artifact, or, if you already have one, you will have to select:
That's for IntelliJ, if you are using a different one, check the official documentation of your IDE.