Learn Dutch: De kat ligt er. - The cat is lying there.

In Dutch, er is often used as the unstressed version of daar (there). You use er when the location has already been mentioned and you are just referring back to it without pointing it out. If you wanted to point your finger and emphasize that the cat is lying 'over there', you would use daar.

Why do we use ligt (lies) instead of just saying the cat 'is' there?

Dutch rarely uses the verb zijn (to be) to say where a physical object or person is located. Instead, Dutch uses positional verbs: liggen (to lie), staan (to stand), or zitten (to sit). Because a cat typically rests flat on its stomach or side, it ligt (lies).

Could I just say De kat is er?

You could, but it changes the meaning! Because of how Dutch uses positional verbs for location, saying De kat is er usually means 'The cat is present' or 'The cat has arrived', rather than describing its physical location in a specific spot.