If this is your first addon, you may be wondering what to do with the zip file. There is a help page here which goes through it, including figuring out where the files go:
https://cartmart.uk/info.php?pages_id=5

General Instructions for what to do in your shop admin to install a payment module here:
https://phoenixcart.org/phoenixcartwiki ... le=Payment

In the module itself, there are descriptions on the settings page which I hope explain what should be there. I have not repeated them in the readme. The readme in the zip file contains the steps you need to go through in Paypal to set up a PDT Identity Token for additional security against your payments being hijacked.

Still stuck? Post a new topic in the addon support forum. Make the subject a short description of the problem you are having so it's useful for anyone else suffering the same issue in future. Include the version of phoenix you are running and whether it was a fresh install or updated from earlier version(s):
app.php/addons/free_addon/paypal_standa ... ix/support