Las expresiones there is y there are se usan en inglés para indicar que un objeto o una persona se encuentran en un lugar determinado. La primera característica de estas estructuras consiste en que there no es el sujeto real del verbo to be, aunque lo preceda, sino que el verdadero sujeto del verbo se encuentra en la posición inmediatamente posterior, por lo cual there no es más que un antecedente del sujeto

1. THERE IS
THERE ARE
HAY

2. affirmative
THERE IS A CAT
THERE IS SOME MILK
THERE ARE THREE CATS
THERE ARE SOME CATS
•THERE IS singular / Uncountable
•THERE ARE plural

3. negative
THERE ISN´T A CAT
THERE ISN´T ANY MILK
THERE AREN´T THREE CATS
THERE AREN´T SOME CATS
•THERE IS NOT / THERE ISN´T singular / uncountable
•THERE ARE NOT / THERE AREN´T plural
contractions

4. INTERROGATIVE
IS THERE A CAT?
IS THERE ANY MILK?
ARE THERE THREE CATS?
ARE THERE ANY CATS?
•IS THERE … ? singular / uncountable
•ARE THERE … ? plural

5. In the fridge
An ice cream
A fish
A coke
A cake
An onion
A pineapple
A pear
An egg
Milk
Carrots
An apple
Lettuce

6. List of things in the fridge
Is there any milk?• Milk
• Fish balls
• Cheese
• Pears
• Onion
• Chicken
• Eggs
Yes, there is.
Yes, there are.
No, there isn’t.

7. List of things in the fridge
Are there any fish balls?• Milk 
• Fish balls
• Cheese
• Pears
• Onion
• Chicken
• Eggs
Yes, there are.
No, there aren’t.
No, there isn’t.