What's the difference between the app embed, the app block and the code snippet? (Essential Estimated Delivery Date app)

All three relate to how the widget appears on your product page, but they do different jobs.

• App embed (required): turned on once in Online Store → Themes → Customize → App embeds. It loads the app on your store and calculates the delivery dates. Without it, product page and cart widgets don't appear. By default, it places the widget automatically inside your theme's product form.
• App block (optional): a block you add to your product template in the theme editor and drag to the exact spot you want. Use it when the automatic position isn't right. After you publish the widget, Reposition with app block in its Placement tab opens the theme editor for you.
• Code snippet (optional): <div class="essential-estimated-delivery-block-liquid"></div>. Paste it into your product template or a Custom Liquid block to place the widget somewhere the app block can't reach.

The app block and the code snippet only choose where the widget goes. The app embed still has to stay on for either of them to work. (The checkout widget is set up separately in the Shopify checkout editor.)