There is There are

"There" is a kind of pronoun used to show something you know exists.

Compare these 2 sentences:
- "A fly is in my dinner."
- "There is a fly in my dinner!"

The first sentence is factual and impersonal. The fly is the subject, and the dinner is the object. In the second sentence the object is "a fly in my dinner", so the subject is "There". "There" functions as a kind of dummy subject that represents a more personal perspective, rather than a factual statement.

Especially in spoken English we usually use the contraction "there's", rather than "there is".