The metric system of measurement is based on powers of ten. To understand the metric system, you should know the meaning of the prefixes to each base unit.
kilo = thousand
hecto = hundred
deka = ten
deci = tenth
centi = hundredth
milli = thousandth
Now, applying these prefixes to length, volume, and mass should be easier.
1 kilometer (km) = 1,000 meters (m)
1 hectometer (hm) = 100 meters
1 dekameter (dkm) = 10 meters
10 decimeters (dm) = 1 meter
100 centimeters (cm) = 1 meter
1,000 millimeters (mm) = 1 meter
1,000 milliliters (ml, or mL) = 1 liter (l, or L)
1,000 liters = 1 kiloliter (kl, or kL)
1,000 milligrams (mg) = 1 gram (g)
1,000 grams = 1 kilogram (kg)
1,000 kilograms = 1 metric ton (t)
A meter is a little more than a yard.
A kilometer is about 0.6 mile.
A kilogram is about 2.2 pounds.
A liter is slightly more than a quart.