Often you will want to pass data from one page to another. You see examples of this without realising it. When using most blogs you will see something like ?p=12 in the URL. This is telling the next PHP page to show certain information.  Most e-commerce sites do it as well.

Create two pages. The first is getsend.html (there is no PHP) which should have this in the body:

<p>What language should be used?</p>
    <li><a href="getget.php?language=english">English</a></li>
    <li><a href="getget.php?language=french">French</a></li>
    <li><a href="getget.php?language=german">German</a></li>
    <li><a href="getget.php?language=spanish">Spanish</a></li>

Now getget.php:

echo "<pre>";
echo "</pre>";
echo "<p>You chose $chosenlanguage</p>";   

Save both and upload then load getsend.html in a browser and hover over the links in turn. Look in the status bar of your browser (normally at the bottom). The ? starts the data which will be sent in the URL. This is a pair of items separated by an equals sign. The first part is like a variable name and the second is the data (or more like an array index and value). The second page will extract those pairs for use.  Click on a link

It is also possible to send more than one piece of data.  Add this as a fifth list item in getsend.html:

<li><a href="getget.php?language=spanish&colour=red">red spanish</a></li>

Now add these two lines below the others in getget.php:

echo "<p style=\"color:$chosenColour\">You chose $chosenColour</p>";

Look at items for sale on sites such as Ebay or Amazon for how many pieces of data can be sent using $_GET and how confusing it can be.  Or how useful it is.