The grid template areas allows you to control the layout of the content by typing in the div types inside of the grid that you set up in grid-template columns and grid-template rows. There are three columns and three rows, so nine spots for content. This gives you the ability to customize the columns and rows by increasing or decreasing them and designate how much of the screen that you want to allocate to a certain div type. For instance the header spans across the entire top three sections of the grid.
The point of this challenge is to show you how to insert blank spaces into the grid. Replacing the word advert with a period ( . ) to designate the blank space. The challenge is a bit silly and obtuse, but if you start using the grid layout there may be times when you want to create some blank spaces in the layout. I think of it kind of like the break line tag in html.