Short code to show post excerpts on homepage?

Hi, I am trying to figure out how to put blog post excerpts on the homepage of my storefront theme. I want to show the newest 4-5 post with maybe 400 characters before it says “read more” and a thumbnail image.

I’ve read up on the short code for this, but it does not seem to work on this theme. I assume I need to add code into the CSS sheet or functions page? Can anyone tell me the code to use, or a link to how to do it? Thank you.