Listen up, it really is that simple! If a sentence has a singular subject it is followed by a singular verb and if it has a plural subject it is followed by a plural verb. Verb and subject must agree.
She likes animals. She like animals.
They like animals. They likes animals.
Sometimes the subject of the sentence is more complex but even then the following verb still must agree with the main noun within the subject. Look at the following example:
The words there and here are never subjects themselves therefore with those constructions (expletive constructions), the subject always follows the verb and determines the number of the verb.
There are many kids in my neighbourhood. There is many kids in my neighbourhood.
There is an apple on the table. There are an apple on the table.
What makes me happy is your smile. What makes me happy are your smile.
What is required are application forms. What is required is application forms.
Collective nouns (nouns with singular form but referring to groups such as team) can be used with either a singular or plural form of the verb., however, it is preferred to use singular verb (in academic writing anyway). Only sometimes a plural form of the verb is required and this will always depend on the context. Compare:
A group of kids have raised their hands. A group of kids has raised its hand.
Coordinated noun is usually followed by a plural verb:
Jean and Tom are sitting at the table. Jean and Tom is sitting at the table.
This is except when the two items are making up a single item:
Fish and chips is a British dish. Fish and chips are a British dish.
When names and titles end in –s we refer to them as a single unit and use a singular verb.
Netherlands has granted US Military use of its islands in the Caribbean. Netherlands have granted US Military use of its islands in the Caribbean.
A number of + noun is followed by a plural verb since the expression is used to indicate more than one of something whereas the number of + noun is followed by a singular verb because the expression is used to refer to the exact number that makes up a group.
A number of people have answered our emails. A number of people has answered our emails.
The number of answers we got was great. The number of answers we got were great.