When you click on the Leganto external tool link in your Moodle course for the first time, you'll see a welcome message and a note that you're about to create a new reading list:
Scroll down to "Create a new reading list from scratch" and click "Create It"
Enter a name (and, if you like, a description) for your course and click "create":
We do not currently have any templates installed, so click on "default":
You now have a blank reading list for your course in Leganto and are ready to add resources.
Watch a video from Leganto demonstrating this procedure (bearing in mind that, unlike this demo, our Leganto instance does not have templates installed):