Apple Pay Cash is now live with the 11.2 update
Apple Pay Cash is supposed to operate just like PayPal and Square Cash. Apple Pay Cash can be used wherever Apple Pay is accepted or you can use it (like PayPal) to send and receive funds. (I have not confirmed personally) but I do not believe you can use Apple Pay Cash with Android users. It is pretty quick to get set up, once you update to 11.2
Apple Pay Cash is ready to go!