The key idea here is that your users will come to your website or use your application to fulfill a certain need. If they can't find what they are looking for, they will leave. In the offline world, people navigate by signs that give them clues to understand their surroundings. When we open a website or an application, we experience them as places. And we start looking for signs, clues, navigation patterns we got used to. That is why you need to care about your website's or application's Information Architecture. There are many elements of the navigation: a logo at the upper-left corner (if you click on it, it takes you back to the homepage - it is a conventional pattern), the main navigation (the main menu), a tag cloud, a search field, list of links e.g. in the footer and so on. To sum up Information Architecture is about how you categorize and organize the information.