When you run your app, it starts a server at your machine, at port 19000 or 19001, to which you will connect using the Expo application, which you can find at https://expo.io/learn, available for both Android or iOS. Install it by following the instructions onscreen:
The initial screen you get when you fire up your app
When you open the Expo app for the first time, it will look like the following screenshot. Note that both the phone and your machine must be in the same local network, and your machine must also allow connections to ports 19000 and 19001; you may have to modify your firewall for this to work:
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