A common problem amongst people new to web development lies in the approach they take to the development of their site. Early on, it's extremely common to have people focusing on coding the page properly and getting the layout on their pages to look just right. Once this is done, there is a tendency to whip together the content, each section with its own page, then make a menu linking all those pages and "voila" you have your website.
Though this approach can work, your end result is going to resemble a bunch of web pages rather than a website. What's the difference you ask? Let's explore the answer.
A web page is a basic unit from which you can develop a website. A web page will commonly have some space devoted to content, some to navigation, possibly some for branding and possibly some space designated for advertising. We've all seen many examples while surfing the web. But a web page on its own, like a single brick is of little value until combined with others. As with brick construction, you can put together groups of web pages any way you like, but in both cases they will be most effective when carefully thought out, planned and interlocked to create a solid structure.
Making sure you've got your web page done properly is still important. Not all web pages are created equal, so it's important to make sure yours is up to par. Despite sharing a lot of similar features, there's a significant amount of variance in web pages on the World Wide Web. Aside from apparent cosmetic differences, there are often functional differences as well. Think of the functionality differences when you visit a page where the main menu isn't located where you expect. It's a subtle difference, but it has an impact nonetheless. Other functional differences can have a much greater impact. Have you even been to a site designed in flash without the flash plugin? In many cases, you are left with only 2 options. Get the plugin or leave the site.