New here

Hi everyone, I'm new to this site. I'm a PM already but I don't have experience with Agile/Scrum yet. I signed up for a 2-day in-person class next month.

I've seen some people reference a scrum guide. What is that and where can I get it?

I've also seen references to PSM certifications. What are those?

Sorry if this is all obvious stuff, I'm just totally new to it all. I want to get as much experience and understanding with Scrum as possible. Thanks!