What will digital contact tracing apps look like and how will they work?

Well, the basic idea is that if you opt in to one of these apps, your phone will use Bluetooth, it will scan, look for other devices that are also being used by people who have opted in. If one of you test positive for coronavirus, the other will get a notification and can then take corrective action. There are a lot of different ways these are being built, but that's the idea.