I used plywood as a material. First, I created a lock system without using glue and bolt for fixing. I fit the pieces together. Then I put a big round piece from the top and surround the other pieces with it.
The views of the sitting tool.
When I turned the round piece the pieces will be locked. Then I put the big round piece on which we sit on the top of the other pieces. So my stool is ready to be sitten.