It's best to start at the Infrastructure manual. Under this unassuming title, you find:
- Developer’s Guide
- IRC Guide
- Python Developer’s Guide
- Core Reviewer’s Guide
- Project Driver’s Guide
- Project Creator’s Guide
- Learn the Gerrit Workflow in the Sandbox
- Test Environment
- Zuul v3 Migration Guide
This gives you a good overview of the code development and testing processes.
Once you have picked projects that you want to contribute to, check if they have their own contributor information, for example Nova. You may also find information about communication channels and contact points in the Wiki, for example, again, Nova.
In general, you should assume that each project works in its own way, but they all should have their meetings in IRC. In case you don't know how to reach a project team, perhaps a message to the developer distribution list helps. Put the project name in your subject line, like so: [openstack-dev] [nova] I would like to contribute to Nova
.