Some examples of subject/verb agreement would be the following:
The teacher grades papers every weekend. (“teacher” = singular subject; “grades” = singular verb)
The house plant has pink flowers. (“plant” = singular subject; “has” = singular verb)
My parents visit my sister in Chicago every summer. (“parents” = plural subject; “visit” = plural verb)
All of the math students have their own calculators. (“students” = plural subject; “have” = plural verb)