The Custom field product block can be used to add additional fields to a product form. This can be used to collect more information. E.g. include a custom engraving field to let customers customize their purchase.

Go to Online Store > Themes > Customize
From the dropdown in the top bar select Product
You may want to create a new product template. If you want your custom field to show up on every product page, use the default product template. Otherwise, create a new template.
On the left-hand side, click Add block then select Custom field
Add a label and check Enable required field if you want to make this a mandatory field
Reposition the block. It’s best to place this just above the Buy buttons block
Hit Save
Start by connecting your source repository and choosing the pages you want to publish.
You can then browse your documentation and ask questions about the content your team has shared.