ord, chunk_split, explode, and implode:

a) ord():
This function returns the ASCII value of the first character of a string.
Example:
$str = "Hello";
echo ord($str); // Outputs: 72 (ASCII value of 'H')
b) chunk_split():
Splits a string into smaller chunks of a specified length.
Example:
$text = "HelloWorld";
echo chunk_split($text, 3, "-");
// Outputs: Hel-loW-orl-d-
c) explode():
Splits a string into an array by a specified delimiter.
Example:
$pizza = "piece1 piece2 piece3 piece4 piece5 piece6";
$pieces = explode(" ", $pizza);
print_r($pieces);
// Outputs: Array ( [0] => piece1 [1] => piece2 [2] => piece3 [3] => piece4 [4] => piece5 [5] => piece6 )
d) implode():
Joins array elements with a string.
Example:
$array = array('Hello', 'World', '!');
echo implode(" ", $array);
// Outputs: Hello World !

mktime, strftime, strptime, and strtotime:

a) mktime():
Creates a Unix timestamp for a date.
Example:
echo mktime(10, 30, 0, 3, 15, 2023);
// Outputs: 1678877400 (Unix timestamp for March 15, 2023, 10:30:00 AM)
b) strftime():
Formats a local time/date according to locale settings.
Example:
setlocale(LC_TIME, 'en_US');
echo strftime("%B %d %Y, %X", mktime(20, 0, 0, 12, 31, 2023));
// Outputs: December 31 2023, 20:00:00
c) strptime():
Parses a time/date generated with strftime().
Example:
$date = "2023-05-15 22:45:00";
$parsed = strptime($date, "%Y-%m-%d %H:%M:%S");
print_r($parsed);
// Outputs an array with parsed date components
d) strtotime():
Parses an English textual datetime description into a Unix timestamp.
Example:
echo strtotime("now"), "\n";
echo strtotime("10 September 2000"), "\n";
echo strtotime("+1 day"), "\n";
echo strtotime("+1 week"), "\n";
echo strtotime("+1 week 2 days 4 hours 2 seconds"), "\n";