We use "there is" when we first mention a singular thing. We use "there are" when we first mention a plural thing. Based on your examples:
There is:
There is a table, four chairs in the room
There is a book, notepads, notebooks on the table
Even though there are multiple items, there is only mention of 1 table, or 1 book first.
There are:
There are tables and a chair in the room.
There are notepads, a book, notebooks on the table.
Even though there is mention of singular items in the sentence. there is a mentions of multiple tables and notepads first. It is about what comes first in the list of items.