Follow go/releasing to launch a new project with a new repository. Once your Ariane launch is approved, fill out go/github/launch to create the new repo. This will create a new empty repository and give you admin access to it. From there, you can push your code and give your team members access. If you would like to manage access to your repo using MDB groups, consider using go/teamsync.
You can request a private (hidden) repository in your Ariane launch to temporarily limit access to just your team, but this should generally be used for days or weeks, not months.
NOTE: Private repos are limited to the googleprivate, or FirebasePrivate orgs.
If you need a longer-term private repo, you can request one.
You must still follow the go/releasing process before putting any code on GitHub, even if it's in a private repository.
Accepting contributions from the community
In addition to the guidance at go/releasing/contributions, external contributers may not have administrative access on your repository. While you may give commit access to trusted contributors, if they will be reviewing and merging pull requests, they must verify that the CLA check passes.