Q: What is the difference between being a project manager a Scrum Master?

Project Managers, in the traditional sense, are tasked with leading projects from a scheduling, budgeting, and resource management perspective. Scrum is about the people, specifically the development team that produces the software.

Scrum masters provide a variety of services and leadership, but the emphasis here (in my opinion) should be on empowering people. It's about the humans who produce the software. If you have unhappy humans, you get bad software.