PHP provides several built-in functions for working with dates and times.

The date() function is used to format a timestamp or a date string. For example, the following code will output the current date in the format “Y-m-d”:

echo date("Y-m-d");

The time() function returns the current timestamp, which is the number of seconds since the Unix Epoch (January 1, 1970).

The strtotime() function can be used to convert a date string to a timestamp.

$date = "2022-01-01";
$timestamp = strtotime($date);

The date_create() function can be used to create a new DateTime object from a timestamp or a date string:

$date = date_create("2022-01-01");

You can use the DateTime object to manipulate dates and times, such as adding or subtracting time intervals, comparing dates, and formatting the date.

$date->add(new DateInterval("P1D")); // add one day
$date->sub(new DateInterval("P1M")); // subtract one month
$date->format("Y-m-d");

The DateTimeImmutable class is similar to the DateTime class but it does not allow to modify the date once it is created.

You can also use strftime() instead of date() to format the date, it is similar but it uses more human-readable format codes, it also depends on the current locale.

The DateTimeZone class can be used to set or get the time zone of a date.

$date->setTimeZone(new DateTimeZone("Europe/Paris"));

It is also worth mentioning the gmdate() function, it works the same as date(), but it returns the date in UTC (Coordinated Universal Time) instead of the server’s local time.

These are just a few examples of the many date and time functions available in PHP. It’s recommended to consult the official PHP documentation for more information on working with dates and times in PHP.