How do you learn about a new industry when starting a job?

So I recently graduated with an undergraduate degree in Marketing.

What do you usually do when you join a company in an industry you know very little about? For example, as a marketing graduate, I might get a marketing role at a company in healthcare, oil & gas, fintech or any other industry. I obviously understand the marketing side to some extent, but I may know very little about the actual industry, its customers, terminology, competitors, and how the business works.

How do people usually go about learning the industry once they start the job? Do you mainly learn through your colleagues and day-to-day work, or do you actively research the industry beforehand/alongside the job?

I'd especially appreciate advice from people who have switched industries or started their careers in an industry they knew nothing about.