We use ‘there is/are’ to say that something exists.
When we use the verb ‘exist’, it implies that the thing’s existence is in question or doubt. So it is correct to say, “I think ghosts exist”, or to ask, “do you think aliens exist?” But it is very odd to say “the pencil exists on the table”. For this, we want to say “there is a pencil on the table”.
Here is how we use it:
Give it a try!