I have the following line of code on my website that won't direct to the mentioned link
<?php
echo '<input name="" type="button" onClick="location.href=\'main.php?user=\''.$_GET['user'].'" style="width: 150px; height: 150px; font-size: 36px; font-weight:bold; font-style: italic;" value="Done">';
?>
Is there anything wrong with the structure of my code?
You have placed the value outside the string, so that the code generated looks for example like this:
onClick="location.href='main.php?user='42"
This will cause a syntax error, and the code will not run.
Place the apostrophe after the value:
onClick="location.href=\'main.php?user='.$_GET['user'].'\'"
typo... you have onCick
instead of onClick
event ;-)