The best way to pay with Bitcoin is to use the app Exodus. You can also buy from within Exodus.
How to buy can differ by region. Coinbase should have worldwide coverage; however if you want an alternative, Google: "how to buy Bitcoin", to get options in your region. Click this link to Google it: search google
You have to send the Bitcoins to your own BTC wallet.
After the payment is confirmed, you can proceed to order and scan the QR code with your wallet app to easily make the Bitcoin payment.