Get more information on your cart page with order notes
Every Shopify theme lets you add a text box to the cart page in which you can capture special instructions on how to prepare and deliver an order. That feature is called order notes.
To enable order notes, go to your Customize theme page, and, in the Cart page section, check the box “Enable order notes”.
You can edit the label that appears above or alongside the order notes box — which usually says “Special instructions for seller” — by going to the Edit language page in the Themes section. Change the words to fit your needs.