how does the question mark work in web pages.?

Question

Example:
www.example.com/page1/topic.php?p=1234

Answer 1

A question mark denotes the separation of a URL and GET data. It is used by a scripting language to generate part or all of the page.

Your example is a PHP page, so for example it would use the data 1234 stored in p.

$getData = $_GET['p'];
echo $getData;
?>

That would output on the page
1234

A more practical example you can see right on this page where it has the value qid, which is the Question ID that uniquely identifies this question and tells the script to open this question specifically.

Answer 2

It marks the beginning of a query string.

Answer 3

i believe it is a place holder, like the address won't except a certain character.... you can type the character in when you type the address (ex. " " ~ ect.) and then when the page loads it converts it to a question mark a default