Hired as a Senior Software Automation Engineer. What should I pick up on?

So I was hired as a Senior Automation Test Engineer that will primarily be using Java. I've been a Software Engineer for the past 5 years and I've primarily used Python (Some Java). The most I've done in terms of "Test Automation" is writing unit tests. I know Selenium is used and I've done a ton of scraping with it.

I made sure the hiring manager was aware that I'm a Software Engineer and haven't formally done any Automation/Test Automation, but he was confident I'd pick up the necessary skillsets. So I wanted to ask you guys, what should I pick up on?

I'll definitely ask my manager, but before my position starts I'd love to read up on some of the core concepts so I'm better prepared for my job. What are the general topics I should be aware of?