Do I have to use Areas?
In a basic multiplayer map the easy answer is NO; but you will want to use at least 1 area designation to tell the game to start with the focus on your starting point. WIthout this area designation and accompanying triggers, the game would start with you looking at a random spot on the map. I'm sure you've seen some user created missions that begin this way.
In a single player mission you will want to use several named areas so the game will know when to create specific types of actions. Your own creativity and planning will determine how many areas you may need.
What is an area?
Areas give you focus for some of your trigger actions, allowing you to create triggers that perform actions based on specific conditions occuring in named areas of your map.
An example of this might be to complete a mission when a players unit moves into an area of the map. Another example, which is used at the start of a mission, is to have it center our view of the map over the dominion (named area) when the game starts.
To create a new Area click on the New Area item and drag and drop it onto the map. You can change the size of the area by dragging the corners of the area. It may take a few seconds to respond once you resize the area, so be patient.
Click on your new area on the map and you will see a menu for Area appear on the right. Name each Area square by typing a unique name into the Name field (i.e. Side 1 & Side 2). In King of the Hill, you see the starting location over the dominion called Side 1 start. You can also see 2 other areas, called Top of the Hill and Defog hill top.
Here is an example of using an Area to show part of the map when the game starts:
Triggers / Condition: Mission Loaded / Action: Defog area over "Defog hill top"