How do I know when I can borrow the book I have reserved?

When a reserved book is available for you to loan, you'll be notified by email if you added your email address when you signed up for Biblio.

You will also get a notification from the app when a loan is ready if you have allowed notifications from Biblio.

If you haven't added an email address when creating your account, you can always add your email address under "Settings" - "Personal information".