I'm currently going through the prep for the PL 200 exam, the first thing that we do is create a screen that has a Gallery control to see a list of data (Customers, Items, etc)
Here are my notes on that subject, I'll add as I go along.
Create a new screen
Add a Gallery control
Set the data source and Layout
Click on the > symbol and set the OnSelect property as shown
Then, set the OnSelect property for the Gallery control