To collect the data from a URL (as below) you would use the superglobal variable $_GET.
You can also use $POST to get the data from a HTTP POST request. $REQUEST contains an amalgam of these 2 variables, plus $COOKIE. Guess what the $COOKIE variable contains... 😃
You may also be interested in the import_request_variables() function, but be conscious of the scope into which you import them - if you do it in a function, those variables will not be available outside that function. This is also a bit of a waste of resources, since the superglobals are already available in any scope, and calling the function will require additional CPU time and memory.
If you aren't sure which one of $GET and $POST to use in a given situation, I suggest you do some reading on some of the fundamentals of HTTP:
Wikipedia's HTTP article
The difference between GET and POST requests
