The keywords noted here are different=distingusiable balls and boxes(you can tell the balls apart)...
Let's say the for balls have color white, yellow, red, and blue... and the boxes are labeled from box 1, box 2, box 3, and box 4.
Pick up the first white ball, I can place it in any of the four boxes, for 4 ways.
Next, pick up the yellow ball, I can place it in any of the four boxes again(since there is no restriction one ball per box)..
Similarly, the same flow for the red and blue balls..
Thus, the answer is 4*4*4*4=4^4=256 ways.
The choices are independent of each other...