I am an absolute beginner, with little to no knowledge on the subject but I have somehow developed a strong interest in theories like String theory and M-theory, by reading about them on other forums. So can you recommend me any farily accessible books or other materials that could help me understand these theories in-depth? Or do I have to extensively study other areas in physics before I am able to comprehend them, if so, what are those other topics?
String theory is not an easy theory, and there's a reason it's not usually taught at undergraduate level. But if you really want to learn more about it, as far as I know, this is the standard textbook: A First Course in String Theory by Barton Zwiebach.