I am not writing a comprehensive tutorial here, though I hope this conversation will help me when I do. This topic is for me to share some of what I have done as I get more familiar with making changes to the seamly2d software. I freely admit there are many things where I am not the expert and invite anyone who has a factual correction to something I say, to SAY IT here, publicly.
I have only a moment right now so I will start with this: @Grace this is the new thread I mentioned to you.
2 things you will need to figure out to start if you want to build a copy of the software that is your own “sandbox” - create a fork from the Seamly2d repository in your own name to keep your changes. Decide whether your local machine is capable and whether you can build your copy locally.
I will write more later and feel free to ask questions.