Start by building Blender, read the docs while it compiles, and dive deep into Blender's architecture.
Contribute by reporting issues, triage bugs from others, test and give feedback on experimental builds.
You don't need to be a developer to contribute to Blender.
One of the goals of Blender development is to be as transparent as possible.
Sharing the notes from meetings, live streaming weekly, and sharing code and design documentation.