After confirming the transaction you'll get an e-mail within a few minutes (this process is automatic) with a direct link to download the mod at the address you have registerd with Paypal.
You can also come back to the website and click the "Download" button of the mod.
In either case you'll be prompted to confirm your e-mail, this is your Paypal e-mail, the same where we sent you the transaction confirmation:
After accepting our Privacy Policy, entering your e-mail address and clicking the "Download" button, the file transfer will start.
If a message saying No purchase made by the given e-mail appears, double-check it's the same e-mail address you get the transaction confirmation at, which in turn is the same e-mail address as your Paypal account.