AP micro/macro?

My son is currenly thinking of taking AP micro/macro in his highschool senior year. He wants to take it beecause economics is such an important issue, but is scared because of the class. He has heard the teacher is very bad and the concepts are quite difficult. Most people get C’s and low B’s and he doesnt want to stress out. He is wondering, if there are any good ways of learning economics. Like an inroduction book or something. He has already bought the textbook for micro macro and is already scared.