I want to make a structure app.

It takes a lot of technology to create a similar app, but the most basic part is the drawing of shapes using Canvas. I think it would be good to start with an understanding of how to freely change the size of the shape and move each object by dragging and dropping.

Canvas is a part of every book that deals with Android, so I recommend you to take a look at the books and Internet resources and analyze the samples provided by the Android developer site below.