The frontend of a website is the part that you can see in your browser, i.e. the HTML/PHP files including all DynPG commands. The backend on the other hand is the administration area of your website, which can be used to create, manage and remove contents. In short: the backend is used for adding contents to your website and the frontend displays these contents.
The wiki area about the frontend has now been completely revised, improved and expanded. You can find out how to create and use the frontend in this area. You will find many useful information about the essential commands fro designing a simple website. You can use this information as a foundation for your own website.