Please see Using git with Angular repositories for details about how we maintain a linear commit history, and the rules for committing.
As a contributor, just read the instructions in CONTRIBUTING.md and send a pull request. Someone with committer access will do the rest.
Change approvals in our monorepo are managed via GitHub CODEOWNERS and are configured via the .github/CODEOWNERS file.
Once a change has all the approvals either the last approver or the PR author (if PR author has the project collaborator status) should mark the PR with PR: merge as well as PR target: * labels.
This signals to the caretaker that the PR should be merged. See merge instructions.
See this explanation.