The subject of a sentence is who or what the sentence is about. The verb tells what the subject is doing. For instance, in the sentence “The dog barked at the cat,” the subject is dog because the sentence is about a dog. The verb is barked because that is what the dog did. Subjects are almost always nouns.
The noun could be singular or plural. Therefore, the verb should be singular or plural as well. So, if the subject is singular, then the verb should be singular as well. That is subject/verb agreement. The subject and verb must agree in number. This only pertains to the verbs that are stated in the present tense. If the verb is in the past tense, then it doesn’t matter.
