Well an HTML page is laid out like a tree.

Each point in the tree is called a Node. The Node directly above another in the tree is its parent (just like a family tree). Any node directly below another is a child

thank you very much
i understood
but i would like to see it a live example
if possible

First, you must understand HTML/XHTML and Javascript. Otherwise you will be trying to run before you can walk.

Then, get your mind round the fact the the Document Object Model (DOM) is a tree structure and learn a few special Javascript commands to address and manipulate the DOM.

There's little point posting examples here as there are several online tutorials which do a much better job. This is one from W3Schools, or stick "DOM Tutorial" or similar into Google.

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