You can add a new event to your calendar in the following way:
In the calendar section (no. 1), we can create a new event/record using the green plus button (no. 2) in the bottom right.
You will then see the window below, where you can fill in all the necessary information and click the create button. The event will be immediately added to the calendar.
There is also another way to create an event: just click directly on the calendar area, which will open the window shown above, and after entering all the data, the event will be created.