First make sure you have added the VeraAlert device successfully (Devices, category Other)
Then create a new scene and navigate to the advanced tab.
There at 'Pick a device', pick your VeraAlert device and press 'Add'.
In the dropdown box select the action you want to execute on VeraAlert and specify the arguments.
The first argument is the message you want to send, the second is the VeraAlertId from your Android app.
Confirm the changes and press the red 'Save' button.
Then, when you trigger the scene, the alert should be sent.
FYI, there is an improved VeraAlert plugin for UI5, but that is not published yet.