The information you see in the “Setup�? field is called “Template TypoScript�? - it is configuration code that TYPO3s frontend engine (extension “cms�?) interprets in order to render the website pages. In the above case the text “HELLO WORLD�? is outputted.
If you know about TypoScript in a historical perspective you know that a) the Setup field might end up being hundreds and hundreds of lines long, b) after a while slightly confusing to manage and c) requiring a lot of TypoScript knowledge, basically all of TSref.
If you know how we did in the MTB/1 tutorial you saw that the amount of TypoScript was not that frightening. In fact we just configured the extension “automaketemplate�? to read an external HTML file and insert dynamic content at certain locations. That configuration was only like hundred lines or so (except menus). Far less than the “nightmares�? of past times.