A has 3 elements, B has 3 elements, so AxB will have
3x3 or 9 elements.

AxB consists of every possible ordered pair of elements,
such that each pair has an element of A as its first number,
and an element of B as its second number. 

I'll color the elements of A red and the elements of B blue, 
so you can see how to make AxB:

AxB  =
  
{1,2,3}x{2,4,6}  =

{(1,2),(1,4),(1,6),(2,2),(2,4),(2,6),(3,2),(3,4),(3,6)}

Edwin