To save a script as an application:

Choose File > Save.

Choose a location to save your file.

In the Save dialog, choose “application” from the File Format pop-up menu.

Enter a name for the script (.app is the filename extension).

Select any combination of options:
Run Only: Saves the application in a non-editable format.
Startup Screen: Displays dialog with the text from the script’s Description field when the script is run. The dialog will also contain Run and Quit buttons that allow the user to stop or continue the script execution.
Stay Open: Causes the application to remain active until you quit it. Choose this option if the script contains an idle handler.

Click Save.