A Reservation marks the time as unavailable but the booking is not confirmed. To do this just log in to your JRNI account and confirm the reservation from there.
To configure JRNI to take Reservations; From the Dashboard, click the Cog/Settings icon.
Click Dept Settings.
Click Change under either Public Bookings or Member Bookings. (JRNI allows you to set specific bookings types based on if someone is a Member who saved login credentials for your Business or not.)
Click Take Reservations.
Bookings will now be taken as Reservations and will require Administrator confirmation from there.