You can add events to your calendar in 2 ways:

OPTION 1: In the "calendar" tab, click on the + symbol at the top right of the screen and select "Event", fill in the information in the partial window and "save".

OPTION 2: In the "Calendar" tab, select the day on the calendar, right click and drag and drop to create the time slot. A list will appear at the bottom and all you have to do is select "New event" and fill in the information in the partial window (as above), then "save".