In an emergency, you can use the spare key as an ignition key.
Take the adapter for the spare key out of the glove box Fig. 1.
Slide the spare key all the way into the adapter Fig. 2. Make sure that the Audi rings are facing upwards.
Press the spare key in the adapter downwards until you hear it engage.
Insert the adapter, spare key first, into the ignition lock. You should now be able to start the engine in the usual way.