Jump out of follow the book mode for a short while. Isolate this inability to correctly locate or write your includes from the rest of your book, get to the bottom of the problem, solve it and then go back.
Create a file called test_include.php
echo 'You have found the test file!';
Then create a file called test.php
Now put those 2 files in the same folder, load up test.php and tell us if the message 'You have found the test file!' appears.
If it does, then move the test_include file to your include folder, then keep messing with the path using the suggestions already given above ..
include 'test_include.php'; // add things to this path - hardcode them at first eg /Wamp/www/includes/test_include.php
until you get the success message back again.
Then take a good hard look at the manual page on includes, and decide on how you are going to handle includes initially.
Come back and ask here if you are unsure what the terminology means, or where the settings are best made. There are many options.