How to nest posts under new pages in Twenty Eleven

Hi – I am not a tech person, have a very simple site in Twenty Eleven which has only had a static about page and a simple main page that I update with new stories.

I’ve added a new page for Poetry, and want to post my poems there – and not on the main page – but can’t seem to find a way to put the Poems under the new Poem page. Everything keeps going to the main page and Poetry is empty.

Surely I am missing something simple? Grateful for any advice.