Sometimes, when developing, you need to know all the php variables of the environment and it is not a simple task to go through all the settings of PHP every time you need this. Here's where the phpinfo() function comes in and saves the day. Phpinfo() would give you all the variables, options, extensions and settings that you wiould need when working on your website.
To find all these out, you would need to upload a text file with any name.php and with the following content:
<?php phpinfo(); ?>
Now you just need to open the file in a browser and have a look.