The easiest way is to start building your first App, and once you get it to a certain point, then duplicate it. At that point Glide will prompt you to either “Copy the sheet” or “Keep same sheet”. If you choose the latter, then both Apps will be sharing the same data source.
It’s also possible to start your second App from scratch and connect it to the same data source as your first App. However, I would recommend the “build one then copy” approach over this, as when you copy an existing App will will get all the screens and computed columns that were created in the first App. So you wouldn’t be starting with a blank slate.
I gave a longer answer to a similar question below: