Question: How do I become a contributor?
Answer: You can join one or more of the WordPress contributor teams.
The #fse-outreach-experiment, which has been running for just over a year, is a good place to start if you want to help test the Site Editor.
Alternatively, you might want to work on: design, development, documentation, translation, marketing, theme review, accessibility, community, plugins, training, meta or any other team.