Er is een kat in de tuin.
English: There is a cat in the garden.
'Er' is a small but important word in Dutch. It is used in many different situations, often where English would use 'there', 'some', or leave the word out. It helps make sentences sound natural in Dutch.
Use 'er' when talking about the existence of something (like 'there is'), when you don't know or mention the subject, with numbers or quantities, and in some fixed expressions with prepositions.
Er is een kat in de tuin.
English: There is a cat in the garden.
Er zijn veel mensen op het feest.
English: There are many people at the party.
Hoeveel boeken liggen er op tafel?
English: How many books are there on the table?
Er wordt hier niet gerookt.
English: There is no smoking here.
Ik heb er drie.
English: I have three (of them).