In order for us to construct an English sentence correctly, we must consider the agreement of the subject (usually a noun or pronoun) and the predicate (verb).
A singular subject agrees with a singular predicate . Also a plural subject (noun/pronoun) agrees with a plural predicate (verb).
Before we proceed on learning the structure, we have to understand first how noun/pronouns and verbs form their plural.
Learning English is just a continuing process - the lessons from the earlier grade levels are somehow the same but became a little complicated as the level goes up. It is a MUST to know the BASIC foundation to be able to adapt in the progress.