Learning A New Codebase? Here's How To Figure Out What Matters
Learn how to blame the code (i.e. know who wrote each line of code)
A lot of people don't realize that when it comes to big companies, there are huge swaths of the codebase where nobody really knows how they work
When absorbing the codebase on a new team/stack, go through the various classes/files in your ecosystem, and use blame to understand the hotspots, the code that's been changed frequently and recently by people. Don't just try to understand the entire codebase straight up.
Use the test plans of connected commits/code reviews to better understand how to run the code and what it does
Maintain the system: This is another reason why you should have great test plans on your diffs/commits, so you can keep your team's codebase well-documented and easy to learn