In the box model, there is a rectangular area defined. Various styles are provided to give shape to this area. E.g. the distance from left, right, top and bottom; the relation of the box with other boxes; its relation with the content in it is defined using CSS.

A box consists of four parts: Content, Border, Box itself or  the page that includes the box.

“Margin” property determines the distance of it from left, right, top and bottom. The distance of the content to the borders is defined by “padding” property. With “border” property, borders of the box are shaped.

For more about the CSS box model, check out http://www.w3.org/TR/REC-CSS2/box.html