In what sense, like, kind of the general process?
The first thing i did after designing the concept was figuring out what key elements i would need to make it work, in this case: mouse/touch handling (to drag stuff around), 2d skeletons and inverse kinematics (to drag whole limbs in a sensemaking fashion), and text and image loading/processing (to make the dolls easier to edit rather than hardcoding everything about how they connect together).
then uh, i needed a lot of help (from tutorials and people) to figure out how to make each of those things work in Godot, largely one thing at a time. past that though, it's just fitting code together like a big puzzle and working out the bugs; i suggest trying to keep distinct systems organized separately as much as possible to avoid getting lost (but also not having so many that it's cumbersome to switch between them)