Plant rose cuttings into a pot filled with propagating sand. Poke a hole in the sand first, so you don't rub off the hormone gel, and then carefully firm the sand around the stem. Arranging flowers seems easy, till you go to do it and realize that what you have made just doesn't have the look you were imagining.
Many of the flower farmers listed here offer a wealth of information on their website, have shops where you can but seeds/tubers/etc ... Place your new cutting in a jar of glass jar full of water, and put it in a warm, bright and location where it can soak up some indirect sunlight. Keep it there until it grows roots that are... Cosmos are one of my favorite cut flowers to grow.