Suppose that you sell a tshirt with the characteristics "color" and "size", and that you have two colors, red and blue, and two sizes, S and XL.
In reality, the tshirsts you are selling (the variants) always have a color and a size, right ?
You sell a blue S tshirt or a blue XL tshirt and not a blue tshirt or a XL tshirt.
So you could have a different price for each variant. Suppose that red coloring is more expensive than blue and that the price also vary based on the size, it could be like that:
blue S shirt: $10
blue XL shirt:$12
red S shirt: $11
red XL shirt:$13