The time function of PHP outputs the number of seconds since the Unix Epoch (January 1 1970 00:00:00 GMT).
The output can be used as a timestamp in database entries, and is very useful for this purpose, as it allows for easy database querying.
<?php echo time(); ?>
Should output something like: 14792462
From unix to readable timestamp
The timestamps produced by the PHP time function can be transformed into "readable" dates with the date function. I.e.:
<?php $time = time(); echo "<p>" . date('Y-m-d', $time) . "</p>"; ?>
The Y represents the year in 4 digit, and the m is the numeric representation of a month with leading zeros, and finally the d represents the day in 2 digits with leading zeros.