Navigate to the Applications folder where you added the Legantoo program file. If you are on the program file, then press the shortcut Command + O to open the program.
When you start the program for the first time, the settings window will appear asking you how to handle your library file and where to save it.
First, you have the option to choose whether you want to create a completely new library or use an existing one. If you choose to use an existing library, you must then choose the location of the existing library. If you decide for a new library, then you can adapt the given directory to your wishes and select your own folder. You can also keep the default directory.
Please note that you must select a folder on which you have unlimited write access. This is necessary for Legantoo to be able to store settings and media in this directory later. The folder specified by Legantoo usually already has these write permissions.
When you have made the settings, click on the OK button. Now the actual user interface of Legantoo opens and you can start your work.