I created this demo in order to ask for help here in Questions but sooner I could ask, I found solution by myself. I’m posting this because I believe it could help other newbies like me 
It’s just simple tool for assembling two basic shapes (I and L) based on position of connection points defined in mesh.metadata
In this demo you can find:
- assembling multiple models
- creating instances
- metadata usage
- picking and selecting meshes
- gizmo usage
- mouse buttons binding
https://playground.babylonjs.com/#XCPP9Y#7616
