There are multiple ways of adding new bookings: click on the add booking button, click on a ghost booking and convert it into a booking or double click on the calendar.
If you hover over an existing booking, on the start/end of the booking you will notice an arrow that will allow you to extend the booking duration.
When creating a booking by clicking on the Add booking button, you can select to add a certain number of hours per day or be more precise and select to book a specific time interval which will be clearly visible if the timespan is set to Day.
The Unscheduled Work area displays all the tasks assigned to a user that weren't scheduled yet (these are the tasks with no start-end dates). You can drag and drop them from here to the actual calendar view and the app will direct you to the user and project it's associated with. It's a great time saver when scheduling multiple tasks.
When dropping an unscheduled booking on the timeline, it defaults to 1 hour for the Day view and 8 hours/day for the 1, 2, 4 weeks view.