The "Create Event Wizard" will guide you through the setting up of a new event file. The "wizard" is shown when you use the menu item File / New Event File.
On this page, the Wizard asks you to configure if this event uses one single map or multiple maps. This configuration is merely setting up the event file initially. You can always reconfigure at a later stage if you find our that your selection is no longer correct.
If you are unsure, you may simply select "one map".
Most events use a single map. The reason for using multiple maps could be that some courses use one map, and other courses use another. Another reason could be that you need two maps to cover the area, and courses may switch from one map to another.
The selection on this page affects the map and control settings for Canvas 1, and possibly Canvas 2 (if two maps are chosen). You can later change the settings by using these dialogs: Canvas / Map - Setup Map dialog and Canvas / Controls - Setup Controls Dialog