We now know how to render content, and how to build a menu; but we still do not have a real website, yet.
We could build a website with COAs, and create the complete HTML skeleton with TypoScript. However, this would be very complex, and prone to errors. If the HTML template file has been built by a template designer and is delivered completely done, it gets even more complicated, especially with slight changes in the layout, afterwards.
Therefore, we have the object TEMPLATE, with which we can parse an HTML template file, and insert the menu, content, and so on, at the right place into it.