Hi Josh,
To automatically apply a discount code on the checkout page you need to prepare following URL
[https://{shop_name}.myshopify.com/discount/{discount_code}](https://{shop_name}.myshopify.com/discount/{discount_code})
replacing shop_name and discount_code according to your needs.
You can also get this link from the admin panel:
Unfortunatelly, I don’t know how to show the discounted prices on product pages. Would love to learn.
HTH,
Lukasz