In this lesson, you learned about the core languages involved in web publishing. While knowledge of these languages isn't completely necessary for producing web mapping apps, you are now likely to have a much better understanding of the pages in which your maps will reside and you'll also be better equipped to develop pages of a higher quality.
In Lesson 4, you'll be introduced to Esri's ArcGIS API for JavaScript and use it to create a map of your hometown.