Royal Road has been the standard beginner text for about half a century, and you won't find many decent card workers who haven't studied it to some extent. And, as magic books go, it's pretty inexpensive, so there's no reason not to pick it up.
There's another contender for best beginner text, though, which is Card College Volume 1 by Roberto Giobbi. I only came to this series when I'd been doing magic for a while, but if I was starting out now, I would definitely want to get this.
So, my recommendation would be to get both of those books, and read them concurrently.