should I use max-width or min width for media queries 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: what is a max and min width media query

/* What this query really means, is If [device width] is less than or equal to 600px, then do */
@media only screen and (max-width: 600px)  {...}

/* What this query really means, is If [device width] is greater than or equal to 600px, then do */
@media only screen and (min-width: 600px) {...}