It's really hard to tell if this is a sincere question. You could always read the Wikipedia page for the R Language if you want to know a little bit about R.
Now, while you can, of course, learn a language for any number of reasons, the best is because you have a reason to. With regards to R, it doesn't sound like you do.
Instead of asking "what is this language good for?" You should ask yourself what you want to do, then find the language that makes that task as easy as possible. Because, at the end of the day, pretty much anything you can do in python, you can do in R, C++, JavaScript, Lisp, Haskell, FORTRAN, COBOL, x86 Assembly, Julia, Visual Basic, or any other Turing complete language (if you're clever and patient enough), and vice versa. It's just that some languages make some jobs easier than others.