Learn Dutch: Er staat geen scooter op de stoep. - There is no scooter on the sidewalk.

In Dutch, when a sentence has an indefinite subject (like een scooter or geen scooter) and describes where it is, we use er as a dummy subject. It works just like 'There' in the English phrase 'There is no scooter'.

Why does the sentence use staat instead of is?

Dutch rarely uses zijn (to be) to say where a physical object is located. Instead, you have to use a posture verb like staan (to stand), liggen (to lie), or zitten (to sit). Because a scooter rests upright on its wheels, it staat.

Why do we use geen here instead of niet?

You use geen because you are negating an indefinite noun. The positive version of this sentence would be Er staat een scooter (There is a scooter). To make it negative, een changes to geen (no / not a). You would only use niet if you were talking about a specific scooter, like de scooter.

Since geen scooter is the real subject, can I just start the sentence with it?

You will almost never hear a Dutch speaker do this. Saying Geen scooter staat op de stoep sounds very unnatural. Introducing an indefinite subject with er is by far the most natural way to phrase it.