They don't hold a car. They hold the reservation and pricing. Many know this strategy and will order a car knowing that the price will go up, but they don't have an intention of buying the car at that time.
To place the hold you need to have your SA or an order specialist make that change. To release the hold, a blue button will show up on your reservation, so you can release it yourself. Towards the end of my 2 year hold, I did get a few notices that they would cancel my order, but I just told my SA I wanted to extend the hold and they were fine with it. Note that I currently have a 2017 Model X, so maybe there was some courtesy applied here, but I doubt it.