PHP is desgined to work in combination with HTML. This video demonstrates various ways in which the two can be combined to display strings, variables, and HTML tags.
A mistake sometimes made is to forget that all files with any PHP code in them must have the .php extension or they will not work. If you name PHP files .html, you will get garbage, so from now on, make sure that whenever you are writing a PHP file, its name ends in .php.
Also – do make sure that XAMPP is actually running or your PHP code will not be interpreted.