how we konw the right way to use is and are and finite and non finite use
If the subject of a sentence is singular, the verb must be singular, i.e. is.
The book is good.
This cake is great!
If the subject of a sentence is plural, the verb must be plural, i.e. are.
The books are good.
These cakes are great!
The verb must agree with the subject in number.
Finite Verbs - Glossary Definition - UsingEnglish.com