I have no experience in teaching but have been requested to teach English including grammar for some school students as I am reasonably fluent in English. I observed that the first chapter in their grammar book starts with Present simple of be (am, is, are). When I studied grammar in school, the first chapter was always definition of sentence, then kinds of sentence, then subject and predicate, etc. I am really confused and wondering how to go about teaching the students. I would appreciate it if anyone could enlighten me as to why some grammar books are different from the other books.

Thanks and regards,