One milliliter of water has a volume of and a mass of One thousand cm cubed of water fills a liter container and has a mass of kilogram I don't get it?

You have your units mixed up. One milliliter (ml) equals one cubic centimeter (cc.) One cc of water at 4°C has a mass of one gram (g.) Kilo is the multiplier that means x1000. Therefore 1000 ml (or cc) of water has a mass of 1000 g or 1 Kilogram (Kg.)