how to insert date and time into phpMyAdmin database, taking dynamically from the user through form.

I assume as you are reffering to phpMyAdmin you are using mySQL database.

To get the current timestamp in a format that is accepted by mySQL date type do the following:

<?php
   $date = date("Y-m-d H:i:s");
?>

This will create the variable date in numerical format that mySQL can understand for example: 2016-03-16 10:44:13.

For more info on the paramerters for the PHP date function check this page from the PHP manual: http://www.php.net/manual/en/function.date.php

If you are placing a user entered date into mySQL you can do the following to convert it into the correct format:

<?php
    $date = "2016-03-16 10:44:13"; // String of the users entered date as example, make sure your form collects the date in this format as a string.
    $date = date('Y-m-d H:i:s'); // Convert string to date format.
?>

You might want to check out this post from a year ago: https://teamtreehouse.com/community/date-from-an-form-into-a-php-script-to-enter-into-a-mysql-database

There are also a number of hits on google if you query php insert date from form into mysql, including this one from StackOverflow: http://stackoverflow.com/questions/30102494/trying-to-insert-input-type-date-into-mysql-column-of-type-date-throws-sql-error