Add text under product category images on Storefront homepage

Is there a plugin, or another way, that allows me to add a block of text directly under each of my 3 product category images on the homepage for the Storefront theme? (4ninths.com)

I’ve got 3 Storefront stock photos there now during development. Above them is the title “Product Categories”. I want to change that title to whatever I want (how?), and I want to add a block of text under each of the 3 photos (how?).

I’d also like to be able to do all of the above for “Recent Products”, etc., as well.

Is there an easy way to do these two things?