Using blocks in Checkout Blocks
Blocks, built with UI extensions, help you customize checkout by providing app blocks that you can drag and drop directly into the checkout and accounts editor. Some block types add visual customization elements to your checkout, such as information and warning banners or line item messaging. Other block types add interactive elements to your checkout, such as variant or quantity selectors for line items, or checkboxes or text fields for customers to select or input additional information.
Although you don't need to use code to customize your checkout, you can make advanced customizations to your block content using some supported Liquid syntax. You might also want to learn more about metafields namespaces and keys, as some blocks (such as the custom fields block) use metafields to store additional data.