I have a question about rounding the edges (of a cube). For example, I have a simple cube. What I don't get is how do I round the edges (like on an iPhone):

[![Smoothed edge][1]][1]

I tried to do something like this, but Picture 2 was the result.

How do I round the ends of my cube like in Picture 3?

[![enter image description here][2]][2]


  [1]: https://i.sstatic.net/PJnyG.png
  [2]: https://i.sstatic.net/vvMHN.png