Folder structure
Inside the freesewing folder -- which might have a different name if that is
the choice you made -- you will find a bunch of files and folders.
The one that matter is the design folder. In it, you will find the following
subfolders:
from-bellafrom-bentfrom-breannafrom-brianfrom-scratchfrom-titantutorial
Remember when you click the Design icon in the header it would bring up this menu:

As you might have guessed by now, each of these options is contained in its
own subfolder under designs.
You can edit the files under designs/[template]/src/ and the changes you make
will be reflected in the development environment.
Don't take my word for it though. Let's start doing exactly that in Part 2.