This series teaches you PHP by building projects that either solve problems, or simulate problems that you can solve. PHP is a language that dynamically builds web pages and is used to deal with data being submitted from a user, or by retrieving data from a data source such as text file or database.
To properly use PHP you need to know HTML, and familiarity with CSS is very beneficial.
PHP is a Server Side Scripting Language. This means the scripts run on the server and the output is sent to the users web browser. The PHP has to be installed on the Server along with Apache or Nginx as the web server.
To build or test PHP scripts as a new coder the easiest solution is to buy a shared hosting plan with GoDaddy or other hosting provider and upload the scripts there. You can run PHP on your own server on either a physical computer, virtual machine, or even Raspberry Pi. To do this you need to know how to install Linux, Apache and PHP. Additionally you need to know how to deal with permissions and navigation for files and folders in Linux.
Since PHP runs on the server and interacts with files and folders on the server you will need to set the appropriate permissions on the server so that files and folders are accessible, readable, and writeable by users.
For creating learning environment you may want to set the HTML folder to be fully accessible by everyone. To do this run sudo chmod 777 /var/www/html .