Web Parts are much like building blocks, they can be easily moved and repositioned on a page. A Web Part can range from something as simple as displaying a title to being a photo gallery or website search. For example, you can select a navigation Web Part, provide properties (like start page on the treeview, define number of levels, repeating direction, etc.) and add it to any page of the site. There is not any development tools or code changes needed at all.
Then, if you don’t like how it fits with the other Web Parts on that page, you can simply rearange them again. And the process is the same for all features and functionality, from basic text content to more robust features like photo galleries, news, products, dynamic or database form creation. With these Web Parts, you have the freedom to design and build (and redesign and rebuild) your site as you see fit.