Can someone explain how you say Ř ř?

i'm teaching myself Czech soon but i can't find an explanation online on how to say the Czech letter Ř ř. they all say, "it's unlike anything in English. it's really hard." or " it's between a ž and an r." but can someone explain what it really is and how you say it? is it like rolling a ž or a š like an r? help!