How to say it in English in class?

If the teacher calls the students to class, it is Class begin, which is an imperative sentence, so there is no S.

If you describe the beginning of the course, you should add an S, such as attending class on time.

English grammar is a series of language rules systematically summarized after learning English language. The essence of English grammar lies in mastering the use of language.

Nouns are generally divided into proper nouns and common nouns. Proper nouns are proper names of individuals, things, places, groups and institutions, and the initial letter is usually capitalized.

Nouns can also be divided into countable nouns and uncountable nouns according to the nature of the things they represent. Countable nouns have singular and plural forms.

Modal verbs themselves have certain meanings, but they should be used together with the verb prototype and its passive voice to add modal color to the predicate verb and show the speaker's attitude and views on related behaviors or things, which are considered possible, necessary or necessary. Modal verbs should be followed by the prototype of verbs.