So you want to potentially contribute to Lyricistant? I'm happy to hear that! Let's help get you started on your journey!
First, it's important to know that Lyricistant builds for Web, Electron, Android, and iOS. In code, these are referred to as "platforms". Every platform includes a core set of common functionality (the common platform) and can also provide platform-specific functionality that makes sense for that platform. For instance, Electron has special logic to handle app updates, while other platforms don't need that logic and so don't include it.
Depending on the platform in question, platform code can run directly in the browser with access to the DOM (Android & iOS), in Node (Electron), or in a Web Worker (Web when running in Chrome or Firefox). This is important as it means that all the common functionality for platforms must be written in an entirely agnostic way. It must assume it doesn't have access to the DOM or Node, and instead use pure ES6 functionality.
On the flip side is the renderer, written using React. The renderer is the code that the user actually ends up seeing. It's the renderer's job to provide information on what the user has been doing to the current platform. Code here should always be written in a way that it doesn't matter what platform its running on, it'll just work. However, it is allowed to do browser and feature checks to work around visual or API quirks in different browsers.
The renderer always runs in a browser, so it has access to the DOM and can use DOM features as it likes. However, due to it not knowing what platform is currently in use, it must always communicate with the platform using only data that is JSON-serializable.
All communication between the platform and renderer uses what is effectively an event emitter system. If you're not familiar, what happens is that platform and renderer code are both given an object where they can both send and listen to events from their counterpart.
An "event" is a channel (which can be thought of as a string key) and some optional JSON-serializable data. JSON-serializable data means that primitives (strings, booleans, numbers), arrays of primitives, and objects with string keys and primitive values are valid, but everything else is not.
For example, the renderer listens for events with the channel of new-file-created in order to know when the platform
has created a new file.
Platforms use a RendererDelegate to communicate with the renderer, and the renderer uses a PlatformDelegate to
communicate with the current platform. We'll get more in depth as to how these work in the
"How Platforms work" and "How the Renderer works" pages.