Adjust the potentiometer to vary the output voltage.
This is a Linear Power Supply Unit (with current limiting) that can output upto 32V at 1.25A (32.5V for a lower output current) and can go down to 0V when the current limit is active (1V under normal operation). The current limit starts kicking in at 1.25A and limits the short circuit current to 1.5A (the lack of sharpness is due to the fact that a single BJT is used for current limiting).
The circuit on the top left is just an AC-DC converter and needs no explanation. The explanation for the voltage regulation circuit can be found here: http://everycircuit.com/circuit/6305068551503872 .
And don't mind the L shaped schematic. I thought that the regulator circuit would occupy more space and started drawing in that way to make space.
