How can I start to develop in mopidy project?

I am an mathematician and an not-very-experienced developer. I want to contribute in Mopidy project, for example there isn’t Mopidy extension for Yandex Music (this is Russian streaming service similar to Google Music, and it has good API) which I can make, but I don’t know where I can start. I know python and popular libraries quite well, but I can’t understand logic of all code that I see in mopidy or in mopidy-gmusic (which I think should be similar to what i want to create). Generally: I love to use Mopidy as user, I can write code, I know what extension I can create, but I don’t know where to start, or what to do. Can somebody give me some advises?

Have you looked at the documentation? There’s a detailed guide on setting up a development environment and explanations of the core concepts.

You’ll also notice there’s already a backend for this:

Yandex Disk is cloud storage like google drive, not streaming service.
Thank you for advise.

I have no idea what it is. The extension’s author wrote that.