Your site have to be structured. Think of a categorize each content document. Later you can provide your visitors with navigators which reflect the actual content of your site automatically. For that you need structure in your site -and for that you need areas.

So think about how you want to structure your site. For our 'cars & bikes' example we have this structure:

Cars<br>
Cars\Alfa Romeo<br>
Cars\Aston Martin<br>
Cars\Maserati<br>
Bikes<br>
Bikes\BMW<br>
Bikes\Suzuki<br>

which means: we have two areas in level 1 and some other areas in level 2. The levels are seperated by a backslash. Theoretically you can use as many levels as you want, but the automatic navigators are currently limited to a depth of maximal 20 levels. If you think you need more than 20 levels, think again :-). No visitor wants to navigate through a site of that deepness...

In every area you can define who is allowed to create and edit content for that area (the editor rights). If you use the work/published workflow you also define who is allowed to publish work versions in this area to the web.

And in the navigation tab you decide if this area is displayed by navigators or not, and if so, you set a position for sorting reaons.

The field 'always expand' is for special use: if enabled the area will always be expanded in navigators (think of a categorized view in which you can define which category should be always expanded).
This is useful if you want to create javascript flyout menus or something like that.

But beside that there are (?URL parameters?) to control which area should be expanded or collapsed.