To pay with PayPal you need to click the "Checkout with PayPal" button (seen below) when on the shopping cart page. This button will then take you though the PayPal express checkout procedure.
1. First Login to your modeltrainstuff.com account and then.
2. Look for this button on the Shopping Cart page when you're ready to checkout:
3. Press the button and follow the PayPal payment process.
If you're still having issues please contact our support team and they'll be glad to help you.