if ($request{'password'} eq $GoodPassword){
Compares the password word typed in the text box on if.html to the password assigned to the variable $GoodPassword.
If they’re the same, then the code between the curly braces is executed:
print "<b>Acme Password verified!</b><br>\n";
TIP: The command eq is used to compare to text variables. Don’t use the = sign—that’s for comparing numbers.