First things first, there is no such thing as “fast”. If you want to start from somewhere, I would recommend to download and read the Scrum Guide. It’s the foundation, the cornerstone of the Scrum framework. If you can’t read sixteen pages, then consider doing something else.
After you have read it, start engaging with the agile community. Go to local meetups, join online forums, read (yes read) books, go to conferences, watch past conferences online. Get experience and keep challenging your knowledge. This is how you will “learn” Scrum and any other agile framework or process. By just reading the Scrum Guide you will get a grasp of what Scrum is but it is not enough. Or by just watching a video online. Or even by just saying that you worked “3 months as a Scrum Master”. And of course, a Scrum Master course is just a beginning. Experience, hard work and willingness to learn is what you will give you an advantage. And lastly, beware of the sources you find online. Similarly, there are thousands of sites who claim that the Earth is flat; it doesn’t mean it’s true though.