An epigraph is a short quotation placed at the start of a poem to help set the tone and focus your efforts. Almost anything can work if you find it inspiring: a quote from another poet, a few sentences from a news article, a memorable phrase spoken by a friend, a saying from Poor Richard's Almanack.
First, pick the quote you want to use, then look at it as you write freely for a few minutes. Next, shape your free writings into a poem, placing the epigraph, with the author acknowledged, between the title and the first line of your poem.
Denise Duhamel's "Buying Stock" is a poem beginning with an epigraph.
Keep your poem between six and sixteen lines long.