What does Formatting string means in PHP?

Formatting means arranging something is a specific way, like to align with columns or putting a number into currency format (with two digits after the decimal point).

Without knowing what you are formatting for or to, it's guesswork..

It could simply be inserting a variable - eg.

echo "Dear " . $name . ", please find enclosed you bill";

For building complex formats, you can use sprintf()

That works in a similar way to the C version - you pass a string containing a format definition, plus the variables you want to include in it.

http://php.net/manual/en/function.sprintf.php

Look through the examples in that article for more info.

Note - They use echo to display the result each time without storing it, but sprintf() just returns the formatted string so you can equally use

$newstring = sprintf( ...

and then do something else with the new string.