The screen on the dash notifies you that an update is available and my phone does also. You need to be near a WiFi point that is connected to your car. If you do nothing, the update will be applied at a time of your choosing that is 11:00 PM by default. You can trigger or schedule the update process from your phone or the car screen any time you won't be using the car for about 50 minutes. On the X, you are warned that the falcon wing doors won't work and the car will be missing a couple features but I think it could be driven in an emergency. Info on the update is available on the screen or your phone but often, the info just states "minor updates & bug fixes" in addition to any major changes that the update brings.
Because Tesla codes their own chips, they are at liberty to change anything they want with an over the air update. Ford, & VW have been very vocal about wanting the ability to do updates like Tesla does but because they farm out chip development, their agreements with chip suppliers don't allow them to access the chips for updates. VW had a major push a year ago, where they formed their own software team to do what Tesla has done, but it fell victim to delays and cost over-runs. It was shut down at a huge loss and efforts have been abandoned and I think they are farming further development out to a Chinese firm. Ford has done no better. CEO Farley has complained that Ford uses chips from 6 or 8 suppliers and none of the chips can talk to each other, so over the air updates are difficult to impossible.