Securing the PCB in the case, and adding keycaps will complete the assembly
Before finishing assembly, be sure to double check the power switch on the bottom side of the Blank Slate PCB is switched to the "On" position.
The specifics of the case assembly will vary by case. For tray mount cases like the Drop Planck case, the only steps required are gently sliding the PCB, USB port first, into the case, and then inserting and tightening the screws through the bottom of the case into the PCB's built-in standoffs.
Once the assembly is secured, add your keycaps to the switches: