"Peter plays tennis"
Peter is the subject of the sentence. The subject is the person (or thing) that does an action.
In our sentence the subject is singular - Peter is one person. We can also have plural subjects (many), for example, animals, cars and towns.
Plays is the verb - it's an action. 'Eat', 'swim' and 'kick' are other examples of verbs.
Subject verb agreement means that the verb we use in a sentence can change depending on the subject. Let's use Peter again:
"Peter plays tennis" is correct because Peter is singular and the verb (plays) is singular.
"Peter play tennis" is NOT correct because the the verb is plural.
To use a plural verb we must use a plural subject:
"Peter and his friends play tennis."
Peter and his friends means more than one person and so it is a plural subject.
Subject Verb Object
It's and Its
Prepositions of Time