Ensuring Subject-Verb Agreement 1
The subject and verb of a sentence must agree in number. That means if the subject is singular, the verb must be singular, too. If the subject is plural, then the verb must be plural.
The pirate sails the seven seas.
(Notice that singular subjects, like pirate, usually don't end in s, but singular verbs, like sails, usually do.)
The pirates sail the seven seas.