A full list of PHP directives can be found at PHP: Description of core php.ini directives - Manual
Every installation of PHP has a default or global php.ini file for the default PHP settings. Normally it is suggested to leave the default or global php.ini file unaltered and to simply create your own php.ini file wherever needed to override the default settings. You can create the php.ini file using a text editor and saving the file to the folder where the settings should apply.
This means that any PHP files in subfolders will not recognize the changes you've made in the php.ini file. You will have to copy the file to any subdirectories needed or created symbolic links in subfolders to the custom php.ini file.
Write each directive along with its value on separate lines. Lines starting with a hash symbol (#) are comment lines and have no effect on the settings within the file.