In English, subject-verb agreement is important. What this means is that the characteristics of the subject should be reflected in the verb. For example, if a subject is a singular, the verb form must also be singular.
Likewise, if a subject is plural, the verb must also be plural.
Unlike in other languages that require that subject and verb agree in both number and gender, English verbs are not conjugated for gender and so require only that they match in number.