You can find Mosspaper's Widget here: https://app.mosspaper.com/d/#/widget. There are 2 sizes available for you to embed into your web site.
1) Log Into your Shopify Account.
2) Select the page you want to display the widget. Click on "Pages."
3) Click on "html".
4) Copy and paste the iframe code into the html code box. Click on "save".