Hi there,
the Mason site is build using the Block Editor ( make sure you DO NOT have the Classic Editor plugin installed ). Simply edit the Home Page, and select any of the Blocks and make the edits you require.
Our YouTube channels has a lot of videos relating to the theme including some videos showing how some of our sites are built:
https://www.youtube.com/c/GeneratePress
Theres not a specific Video for Mason but there are others such as Crypto which will give you a good understanding of how they are constructed.