Customizing the Woocommerce Storefront theme

I’ve created a child theme of the WooCommerce Storefront theme and would now like to customize my front page. (Specifically, I would like to add some sections under the product categories – some images, extracts from my blog and an advert.)

I’ve taken a look at template-homepage.php and can see that I should make use of do_action to be consistent with the existing code. And I have a vague idea of how it works.

But…. where do I find the code for these hooks? For example, in which php file is the storefront_product_categories action defined?

Thanks.