The h-offset casts a shadow either to the left or the right of the box by X number of pixels. Use a positive value to go right and a negative to go left. on here the box-shadows' horizontal properties are set to 150px (going right) and -10px (going left)

The v-offset works much like the horizontal property except vertically. positive vales cast the box-shadow downwards and negative values cast it upwards. On this box we are using the vertical values of 10px (going down) and -120px (going up)

The blur property smooths out the shadow so it fades into the background. The value set for the blur determins how gradually it fades. The two previous examples had no blur applied, this is what it looks like with a blur of 20px applied to the right box shadow and 100px applied to the left box shadow.