...same thing it would do for any other muscle I believe..
What "tones" the midsection is low bodyfat..higher levels of development will have them show through easilier so it will appear "toned" faster...bigger too.
If you're flexing them then you might be stimulating the transversus abdominus which is the "inner slab" basically...that can tighten things up..but you don't have to do that all day, you can work it properly with its own list of exercises.
The shape of your abs is because of genetics, you can't change their shape by favouring one leg while running.
"I don't like misplaced apostrophes"