It is a frequent necessity to transfer variable values between pages. You may have an HTML <form> which asks for user input to named fields. These fields (as well as hidden variables) will be transferred to a PHP page for processing. This may be the same page that defines the form, or a different one. A method of either 'post' or 'get' must be given in the form tag.
Another way to transfer variable data to another page is make an HTML link (such as with <a href="target_page.php?var_name_1=data&var_name_2=data">click this link</a>).This of course can be entered on the browser's address line, too. This information (the stuff after the ?, or "var_name_1=data&var_name_2=data") is known as a URL Query String ("UQS") and can be treated like a "GET" form submission.