For singular nouns, the verb must match in number.
Example:
My singular noun example is a cat. I is a good example of subject-verb agreement.
For plural nouns, the verb must also match in number.
Example:
My plural noun friends and I are having fun.
Collective nouns are a special case. They can be singular or plural.
Example:
My team is working together. But, my team is not working well together.