The structure of your website is the way your web pages are organised. If you have very few pages (for the sake of SEO, you shouldn’t be having too few pages by the way) you can have a flat structure of your website where all the pages reside in your root directory. But if you have many pages, say 30+ page, I recommend you organise them under various sections/categories so that it becomes easier for you to manage them and help search engine crawlers and human visitors go through your website in an organised manner. And example of a website structure is:
As you can see, there is a root page, what they normally call the home page. The home page might lead to many categories but to keep the graphic and the example short I have drawn just two categories. Category 1 has various pages under it (there can be numerous page but I’ve drawn just two). Category 2 has a page and a sub-category named Category 2->1 and this category can further have many pages.
Do not create deep Website structures
When creating your directory structure, take care that you don’t create too many sub-categories under too many categories and sub-categories. At the most, keep the depth till two levels, like shown in the above image: Category 2 and then Category 2->1. Try not to create Category 2->1->1 and then Category 2->1->1->1 because then the search engine crawlers leave your website without digging deeper. Most search engines don’t go beyond one or two levels of directory structures.
Use your keywords to define your website structure
Use your keywords while naming your directories and files. For instance, a URL like http://www.yourdomain.com/web-designing/e-commerce-web-designing/ is far better than http://www.yourdomain.com/category1/showfile=4.
Make cross-structure navigation easier
Make sure your visitors can easily jump from one category to another, without having to click the Back buttons multiple times. This is why it is important that you list all the top category links somewhere prominently on every page. In fact if you are planning to have a complex structure, then you should create a drop-down menu with as many sub-menus as needed so that with just a simple click or with very few clicks any page can be accessed.
Your website might be having great information, but if that information is not logically organised it will be very difficult for your visitors to access it. Make your information easy to access and your visitors will come to your website again and again.