Add lines of text to Checkout process

[SwissArmyKnife]

Hi. I created a child theme. I need to insert lines of text into specific places on the pages of the Checkout process. For example, I am using Static Shipping; before the shipping locations, I need to insert text to clarify the importance to the shopper to pay close attention to the options. Which PHP script(s) do I need to copy into my child theme?

Thank you.