reading this https://developers.google.com/in-app-payments/docs/tutorial
Quoted from the above page: Because you sign the JWT using a secret key (the Seller Secret), you must generate the JWT using server-side code. It's simplest if you use a library.https://github.com/luciferous/jwt
Must I somehow include this...? I so how? there is more than one file there and no read me of what they each do, I am very confused!
The docs just don't say!
To quickly test the JWT functionality you only need to include luciferous/JWT.php
You include library files using the PHP require_once or include_once statements. Have a look at the luciferous/tests/Bootstrap.php and JWTTest.php for an usage example.
The other files you mention are used to create the PEAR package (PEAR = PHP Extension and Application Repository). You can read more about PEAR here.