The PHP scandir function is a built-in function that allows you to scan a specific directory and return an array of all the files and directories contained within it. It is commonly used to create a list of files and directories that can be accessed and manipulated by other functions or scripts or to check if a particular file or directory exists within a specific directory.

To use the scandir function, you must specify the path to the directory you want to scan as the first argument. For example, to scan the current directory, you would use the following code:

$files = scandir('./');

This will return an array of all the files and directories contained within the current directory, sorted in ascending order. If you want to sort the array in descending order instead, you can pass the second argument “descending” to the function like this:

$files = scandir('./', 'descending');

Here is an example of how you can use the scandir function to list all the files and directories in the current directory:

$files = scandir('./'); 

foreach($files as $file) { 
echo $file . "<br>"; 
}

This code will output a list of all the files and directories in the current directory, with each item separated by a line break.

Note that the scandir function does not scan subdirectories by default. To scan subdirectories, you will also need to use a recursive function or the glob() function.

Overall, the scandir function is a useful tool for scanning and manipulating directories and their contents in PHP. It is easy to use and can save time and effort when working with large or complex directory structures.