Insert Date & Time

wordpress functions
the_time() and the_date()
http://codex.ww.wp.xz.cn/Function_Reference/the_time
http://codex.ww.wp.xz.cn/Function_Reference/the_date

or do you mean the time when the page was called from the server?

<?php date(); ?>
http://php.net/manual/en/function.date.php

or time as in clock – ticking along?
would need a simple javascript – search the web, for instance ‘javascript clock’