OK, kiddo. Brahmarakshasas are creatures from Indian mythology. According to the stories, they used to be humans, but they did something really, REALLY bad, and as a punishment they were turned into these scary monsters. They're often described as having a human body with a lion's or tiger's head, and sometimes they have wings, too.
Now, these creatures are said to roam around in the forests and jungles of India, and they're supposed to be pretty fierce and powerful. They're said to be able to fly and to have super strength and super speed. Some people believe that they can even cast spells or curses on people who cross their paths.
But here's the thing, kiddo: Brahmarakshasas aren't real. They're just stories that people tell to scare each other, kind of like ghost stories. So you don't need to worry about them actually existing and coming after you. Just make sure you don't do anything bad enough to turn yourself into one!