It means that 1 liter of a liquid contains 1000 milliliter of the liquid. In other words, in 1 liter there is 1000 mL of the liquid. And milliliter means one thousandth of a liter.
So when we pour 97 mL of the water in a jar which has a capacity to fill water up to 1 L or 1000 mL, the water filling the jar will come close to the bottom of the jar which is approximately 100 mL . It will rise up to the mark which reads 100 mL in the jar that is graduated.
When dividing indices with the same base, the rule is to subtract the index of the denominator from the index of the numerator, and to keep the base the same.
In this case, the index of our denominator is 6, and the index of the numerator is 2.