Embedded systems and OS programming

Question

Hello. Im really interested into system programming. I tried few languages but ended up with C. I really love low level stuff and I know that's what I want to do. But OS programming isn't that popular and common topic like for example web coding. I know it's hard but I would really like to start somewhere. Just some "basic" IO system. Tutorial, course or book, anything that will help. (Also is there any difference between embedded systems and operating system? I found some udemy courses but I don't exactly know what will I do in that) Thanks