There is a doctor next door.   Is the doctor in his office?

So many things go back to your understanding of definite and indefinite articles. Want to see that again that quickly? (If you do, remember to click "back" at the top of the page to come back here).

Contractions

Add "s" or "'re" to the there, depending on the person.
There's a new doctor in town. There're 2 new doctors in town.  (Note: Many native speakers will prefer to say There are rather than There're because the 2 final "r" sounds are difficult to say. But watch for it both ways.)

Negatives and Contractions:

For a negative simply add not right after "is" or "are." Always.
There are not 5 pencils in my purse.
There is not a doctor here.

And contract them in a usual manner:
There aren't 5 pencils in my purse.
There isn't a doctor here.

So we use "there is"  commonly and correctly every minute of daily talk. Most native speakers don't think about whether a subject is definite or indefinite. But you must....

Now, try to make a There is/There are question. Have fun!