The narrow strips of wood from the ripping will eventually form the stiles of the front of the cabinet.
The sides themselves, need a dado for the shelf. I am just going to put in one single shelf in the middle of the cabinet, though you could also put in more shelves if you wanted to. I guess that two shelves would be the maximum practical number, to prevent the height between each shelf to become too low.
Technically there is nothing wrong with putting the shelf other places than in the middle, but since I don't know what I'll use the cabinet for, I'll go the conservative and safe route.
Since I don't have a dado plane, I usually make my dadoes by marking them up, and sawing to the desired depth. A fine crosscut saw is ideal for this job.
I normally clamp a piece of wood right next to where I am going to make the cut, to help guide the saw.
Once I have made the cuts, I remove the waste using a chisel and then I clean up the bottom of the dado with a router plane. If you have a real router plane i.e. a plane which is easier to adjust then my homemade router, It is easy to remove all the waste using such a plane. Just remember to gradually increase the depth of your cut. You'll be able to control the router plane better if you don't take a huge cut such as 1/4".
The top and bottom needs some rabbets. The design calls for approximately 1/4" of wood to protrude from the carcass as a decorative element.
Since I am going to try making blind dovetails, my rabbets on the sides will have to be 11/32" wide (9 mm) That way I can have 1/8" of wood left to cover my dovetail and still meet my design criteria of 1/4" protrusion.
The rabbets on the front will need to be 1/4" plus the thickness of the sides themselves (3/8") = 5/8" wide.
For all the rabbets I used my rabbet plane, but if you haven't got one of those, you could also make them the same way that I made my dadoes. But that would probably require a bit extra sanding eventually.
Sawing the sides of a dado.
Cleaning out the waste from a dado with a chisel.
The rabbets on the top and bottom boards.