You can now add products to your Stripe account, which will show up in the Payment for Stripe app. You can start by logging in here (the experience is optimized for your desktop, at the moment):
From there, you can choose to "Add Product". Then, select "One-time" to add the price to the Product. You may also find it helpful to add a "Price Description" as well, as these descriptions will be displayed in the Payment app.
If you'd like to add more Prices, you can click the "Add another price" button at the bottom, or navigate to the recently created Product and select "Add another price" on the right.