There is the notebook.
The book is on the desk.
I am on the chair.

==========================

1.
Anna: There are the notebook.
Correct: There is the notebook.
Explanation:
*We use the following words depending on the number of the subject.
There are + (many things)
There is + (one thing)

2.
Anna:   book on the desk.
Correct: The book is on the desk.
Explanation:
*Start the sentence with an article (a/an/the).
*Don't forget to write a linking verb (is/are) between the subject and the rest of the sentence.

3.
Anna: I am on the chair.
Correct: No correction

==========================

Hello, Anna! Thank you for submitting your homework. Please read the following corrections and explanations carefully. If you have questions and clarifications, you can ask me in our class. Thank you!