Optional: Since you're WordPress site is likely empty, and it's hard to create a theme when there's no content, you can download sample content (and import) for development purposes.

No need to touch the theme code. Here's how you can set up a child and block theme in WordPress without the hassle.

How to Add a Custom Text Box Before an Entry in WordPress. Add a text box before each of your WordPress posts to expose more of your customers to your business's special offers or latest news.