Question about GSoC 2021 project?

Hey! I want to work on the "Real-time collaboration on a note" app under GSoC and I understand what to do but I am not able to understand your API how do I start with it cause the project requirement is that I need to make a note app with Joplin API and add real-time collaboration feature in it. Is that I'm right?
So, can anybody help me, how do I start with your API step by step?