초보
1 . 처음으로 내딛는 걸음.(The first step)
2 . 학문이나 기술 따위를 익힐 때의 그 처음 단계나 수준.(early stage, beginner level)
초보자
초보의 단계에 있는 사람(beginner, novice)
Originally, 초보 has no meaning of beginner. But, nowadays, 초보 is also used as a short form of 초보자.
So, 초보 can be mean "early stage, beginner level" as well as "beginner"
초보자 only means "beginner"