Study the prefix centi. Centi stands for one hundredth of something. So, the term centimeter means one one hundredth of a meter. In other words, there are one hundred centimeters in a meter.
Study the prefix milli. Milli stands for one thousandth. So, the term millimeter means one thousandth of a meter. In other words there are one thousand millimeters in a meter.
Study the prefix kilo. Kilo stands for one thousand times as much. So, the term kilometer means one thousand meters. Likewise, a kilogram is equal to one thousand grams.