when to use min and max in css media query code example

Example 1: media query min and max

/* Max-width */
@media only screen and (max-width: 600px)  {...}

/* Min-width */
@media only screen and (min-width: 600px)  {...}

/* Combining media query expressions */
@media only screen and (max-width: 600px) and (min-width: 400px)  {...}

Example 2: media query min max

@media screen and (min-width: 200px) and (max-width: 640px) {
  .bloc {
    display:block;
    clear:both;
  }
}