I have no clue how to do the double displacement method thing so if anyone wants to help me that would be great :-)

The question is:
Write the complete ionic equation for the double displacement reaction that occurs when aqueous solutions of barium nitrate, Ba(NO3)2 and sodium chromate (Na2CrO4) are mixed.

I didn't understand it when we did it in class and when I went to her for help she refused to help me