PHP Fatal error: Call to a member function format() on boolean

Neither example work as you have multiple errors:

1. You forgot your second parameter to Datetime::createFromFormat()
2. h:i:s should be H:i:s
3. Your date in the second example is separated by a . not a -

Fixes:

<?php 
    $date = "13-06-2015 23:45:52";
    echo DateTime::createFromFormat('d-m-Y H:i:s', $date)->format('Y-m-d h:i:s'); 

    $date = "10.06.2015 09:25:52";
    echo DateTime::createFromFormat('d.m.Y H:i:s', $date)->format('Y-m-d h:i:s');
?>

You need to convert it to something you can use for further formatting. strtotime() is a good start, which yields a unix timestamp. You can format that one using strftime() then.

strftime("%d-%b-%G", strtotime($ts));

As I stated in comments, you didn't choose a database.

As requested:

This line:

$db = new mysqli("localhost","root","");

Should have read as:

$db = new mysqli("localhost","root","", "database");

and replacing "database" with the name of your database.

The documentation can be found at the following address on PHP.net:

• http://php.net/manual/en/function.mysqli-connect.php

Example pulled from the manual along with error checking:

<?php
$link = mysqli_connect("127.0.0.1", "my_user", "my_password", "my_db");

if (!$link) {
    echo "Error: Unable to connect to MySQL." . PHP_EOL;
    echo "Debugging errno: " . mysqli_connect_errno() . PHP_EOL;
    echo "Debugging error: " . mysqli_connect_error() . PHP_EOL;
    exit;
}

echo "Success: A proper connection to MySQL was made! The my_db database is great." . PHP_EOL;
echo "Host information: " . mysqli_get_host_info($link) . PHP_EOL;

mysqli_close($link);

Note: Alhough you can still theoretically connect, you just wouldn't be able to query anything though. That's where error checking is important during development testing.