At the bottom of the sidebar you'll find the "current guests". There you'll find all guests that are currently checked in, will check in today or will check out today. This will list all guests, main contacts as well as companions.
You can sort this list by its columns (ascending and descending) by clicking on the column headers.
Pressing the button Arrival Today will show you which guests are due to check in today, pressing the button Departure Today will show you which guests are due to check out today.
Guests that are overdue will be marked in red in the Arrival Today area.
If there is a note for a guest that appears in this list, the symbol will appear next to their name. Double-clicking on the symbol will take you to the guest notes.
Guests who are regulars will have the icon next to their name.