Single and Dual Help?

I just got a motherboard that has dual channel slots for ram...the max ram the board can hold is 8bs in each slot with 4 slots. I want to put 8gbs of ram into one slot that possible or do I need another stick?? If so can I also do that with the other two slots and put in a stick of 4gbs in there that I'm getting from my old computer? So together I have a dual channel motherboard with four slots and a stick of 8gbs and a stick of 4gbs and i want to put them in my let me know how I can make this work?

Reply ASAPĀ 

the RAM probably won't match up. it's best to buy a dual-channel kit, then you KNOW that they will work with each other