Fist cut out the back of the shelf then make two more copies of the shelf sides.
Then add the 3sides then tape or glue them
Then place the shelf on a piece of the board then trace it and cut it out
Then with both of the top and the bottom and tap or glue them
Then cut a piece then tape or glue it on
Then test to see how sturdy it is
The creator of this guide has not included tools