New Job - What Do You Master First?

Sorry for the lack of updates for the last 12 months; I finished up at a place I was at for almost six years, spent 7 months at a different place, then changed yet again. Today marks exactly two weeks since I started at my new place.

So - what do you master first at a new job? What do you make a top priority in scoping out?
What is the first and foremost necessary skill needed to survive a new workplace?

If you have a CM/DevOps bent, you might say "the build system" or "the source control toolset". If you're a developer maybe "the software development lifecycle" or "the nearest Five Guys or In & Out".  Finally, if you're in QA/SA, you might say "the defect system" or "the test case management tool".

As I mentioned earlier, today marks my 2 week anniversary since starting here, and I've mastered the most important and foremost necessary survival skill -

Upon opening the door & taking a single (silent) step inside, I can immediately tell which stall doors are closed and locked (and occupied) versus empty stalls that have swung shut on their own, on the three closest restrooms to my desk.
The results of said single glance will determine if I continue into the restroom or depart as silently as I first arrived.

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I'll try to be more dutiful with updates for the rest of this year. Thanks everyone!

-Kelly