Textbooks are mandatory reference books used in schools that contain learning materials in improving faith and piety, character and personality, the ability to master science and technology, sensitivity and aesthetic abilities, physical potential and health compiled based on national education standards.

The function of the textbook
Judging from the content and presentation, the textbook serves as a manual for students in learning and for teachers in teaching students for certain fields of study or subjects.

A study guide for students means using it as a main reference in:

prepare yourself individually or in groups before learning activities in class
interact in the learning process in class
do the assignments given by the teacher, and
prepare for formative and summative tests or exams
For teachers, textbooks are used for reference in:

make learning designs
prepare other learning resources
develop contextual teaching materials
give assignments, and
compile evaluation materials