Use there is or there are, here is or here are depending on the subject that follows the verb.

Examples:

There are new discoveries every minute of the day.

Here is a basket of apples for you.

Using a prepositional phrase instead of there or here does not affect the verb form.

Examples:

In the room are five babies.

At the ground floor is a man trapped in the elevator.

Never change it is to it are.

Example:

It is good to know about your discovery.

A collective noun used to denote a unit uses a singular verb. It takes a plural verb when it is used to refer to individual members of a group.

Examples:

The audience listens attentively to the lecturer.

The audience react differently to the lecturer's statement.

The class accepts Jesse's apology.

The class have opposing opinions regarding Jesse's explanation.