The subject of a sentence is what the sentence is all about. In the following sentence, the word "book" is the subject: "The book is on the table." In this example, the focus of the sentence is the object in question: the book that sits on the table's surface.
The verb of a sentence is the action word that generally describes what the subject is doing. In the following sentence, the word "walks" is the verb: "The man walks to the car." In this sentence, the verb "walks" describes what the subject "man" is doing.
In all English sentences, both the subject and the verb must agree with one another. Depending on whether or not the subject is singular or plural, the verb must match that subject(s) and/or object(s) accordingly. For example, if the subject of the sentence is singular ("the man") then the verb that describes what the man is doing must also be singular ("is," "sits," "eats," "smiles," etc.). If the subject is plural ("the men"), then the verb that describes the subject should also be plural ("are," "sit," "eat," "smile," etc.).
If the subject of the sentence is made up of two or more nouns, then the verb should be plural. In the following sentence, for example, the nouns "man" and "woman" are the subjects, and the verb "are" is the matching plural form: "The man and woman are in their house."
If there are two singular subjects in a sentence connected by the word "nor" or "or" then the corresponding verb should be singular. For example: in the following sentence the nouns "table" and "chair" are the subject and the verb "is" describes their action: "The table or the chair is sitting in the kitchen."
In spite of the way they sound, the following words: "either", "neither", "anybody", "anyone", "nobody", "somebody", "someone", "each", "each one", "everyone", "everybody", and "no one" are actually singular subjects that require a singular verb.
Nouns like "pants", "scissors", "shears" and so forth are are two-parted objects, and as such, require a plural verb.
Collective nouns like "family", "group" and "committee" are subject words that imply more than one person or object, but are still considered singular nouns. As such, they require a singular verb to describe their action.