Scrum is one of many implementation / interpretation of Agile.
Agile(Agile Software Development) is all about being the ability to make changes in your direction (It’s not about being fast)
Agility is achieved by short feedback loops and Scrum is one systematic way of getting those short feedback loops.
Why Learn Scrum?
you might be a developer that will be joining a team that uses scrum (very common!), you may be a non-tech person hoping to join a devteam to get started with roles like QA,Product management, project management.
Or you may just want to learn scrum and implement it in your worker (yes scrum is not just for software development).
Before you start with scrum, read about the Agile Manifesto first
Next you can take this 10minute crash course on scrum
Last, get this comprehensive Scrum guide
so you can have a guide for each of the Scrum Roles, Events and Artifacts.