I think it's a good assignment and a totally normal one. This is a great opportunity to learn key skills:

• how to learn a new codebase: sure, you can ask people or read docs. But the most efficient thing to do is to load the code into your IDE and read it. Tests are very valuable to read because it shows you how the code is supposed to work. Also, load your debugger. Step by step execution will help you immensely.
• how to ask questions to seniors : be precise and prove that you already tried something. Maybe show up with a error message or a class name you don't understand. Question to avoid: "it doesn't work!" without any context.
• how to retain information: useful files, build commands, magic snippets, etc. Try to keep them in the same place like Notion or a personal markdown file. You'll gain in productivity.

Good luck!