Containers are a type of Control that can contain other Controls. By adding child Controls to a Container Controls you can group together Controls for styling and structure.
You'll find structural containers in the Containers section of the 
Palette, the most basic of which is the 
Panel Control which represents the HTML <div> tag.
The Landmark Containers section has accessiblity-orientated Container Controls that assistive technologies built into modern browsers, can use to interpret your content and help with navigation within the page.
All Container Controls have a Layout property that defines the way it displays its children.