Some common Libraries are predefined in Memento Database. In order to ease the creation process, you can choose one of them and adjust as you wish. To create a new Library based on the skeleton, choose Add Library option from burger menu at the top-right of the window and choose the one from Templates section.
Now you can edit each and every setting and field. To learn more about specific tabs and adjustments, follow the links: Fields, Aggregation, Autofill, Main Library settings.