HTML is the basic structure of your webpage and then CSS is the style added to it. So most anologies that include building something can work. For building a house the blueprint, foundation, framing, walls, roof, rooms, would be HTML and then the decoration like paint or types of carpet would be CSS. comparing it to a person, their bones, skin, muscles and organs are HTML whereas the clothes they wear, style of haircut, and type of perfume they use, would be CSS.
The DOM is a little harder to incorporate into these analogies but let's give it a go... The HTML is the initial blueprint that wont change but the DOM is the implementation of that blueprint when building the house. It can be done in different ways depending on who is using it but any changes made wont affect the initial blueprint.
Boxifying is the process of breaking down a web-page design into a series of individual boxes, making it easier to understand.
The Box Model consists of margins, borders, padding and content. Together they make up every HTML element on the page. Each of these can be adjusted to create different styles, effects and spacing.