The Valor Fitness SQ-BOX Adjustable Squat Box is a strong piece of workout equipment with a 17.75" x 17.75" top platform that teaches you to sit back into your squat. This is vital for squat help, by improving your squat performance while also serving to prevent injury.
The difference between free squats and box squats is pretty simply: instead of moving directly from eccentric phase (the descent into the squat) to concentric phase (ascent from the squat) in a free squat, now you squat directly onto a platform between the eccentric and concentric phase. In free squats you can take advantage from the spring of the eccentric phase to almost bounce back to the top. But with box squats, you no longer have this advantage and instead you are forced to begin your ascent back to the top of the rep from a stopping point with no momentum - this will directly increase power and explosiveness of your posterior chain so you can explode out of the bottom position in your free squats.
With this in mind, Make sure to keep in mind that box squats should supplement your training, rather than replacing free back squats.