In order to perform PayPal testing, you must first need sandbox accounts. Sandbox accounts act as real accounts but the transactions that happen are not actually monetary - they only demonstrate the transactions. You can simply create them by browsing to Accounts in PayPal Developer Dashboard. PayPal Developer Documentation has numerous useful documentations for developers.

Make sure to create both a buyer(Personal) and a seller(Business) accounts.

Once the sandbox accounts are set up, you can use the following template to implement the "Buy Now" button.


You can alter the values of item and amount to be directed from the item details and proceed.