Getting feedback on pd150

Question

i have a pd150 plus i have placed the speakers in front of my system and still getting feedback. so i purchased a floor monitor in order to be able to hear what my small church croud is hearing. now i do not know how to hook them up . there is an in and out on the monitors but how do they hook to the pd150. i have the cables. what do i need now,i did not know it would be necessary to have monitors, now that i have them i would like to be able to use them. please help thank you