The leading of these global variables is $_SERVER. We can access the server data and the IP address and browser data of the visitors.
To handle all the values of the $_SERVER array, let me tell you what it is by simply printing it to the screen with print_r():
Note: I have omitted some values that I do not need to explain and that you will not need to use yet.
Array
(
[HTTP_USER_AGENT] => Visitor browser information
[SERVER_NAME] => Name of server
[SERVER_ADDR] => Server IP address
[SERVER_PORT] => Server port
[REMOTE_ADDR] => Visitor's IP address
[DOCUMENT_ROOT] => The file's home directory
[SCRIPT_FILENAME] => Array address of running script
[REQUEST_URI] => Which address it is currently in
[SCRIPT_NAME] => Name of working file
[PHP_SELF] => This is the name of the working file
[REQUEST_TIME] => Current time
)