Amd a8 3870k and sapphire hd 6670 ddr5 crossfire

Hi guys..

Can amd a8 3870k crossfire with sapphire radeon hd 6670 ddr5?

I don't know much about crossfire and I was wondering....

A.) How would I know when there is crossfire?
B.) How to crossfire?
C.) will it automatically crossfire when I install the GPU? Or I have to do it myself(Question B)?

My motherboard is Gigabyte A55M-DS2 .. It says that it support DUAL GRAPHICS.