The SKU is just a way to keep track on the back end of which variant is which. To show you an example with your options.
JFP18x10,5.00,1,10,James Family Portraits,1,8x10
JFP111x14,8.00,1,10,James Family Portraits,1,11x14
So in this example I enter an abbreviated form of what is being sold for the SKU JFP(James Family Portraits, 1(photo number 1), 8x10(the size).
Next comes the price, in this case I just used $5.00 for the 8x10 and $8.00 for the 11x14
After that the weight in ounces
Then quantity in stock
The last three will be your options, shown as which variant is being pointed at, in this case an 8x10 photo of the 1st picture form the James Family Portraits folder.