Kilograms are like half of a pound. But they are in metric form. Pounds are customary and used only in the United States and parts of England. Metric is used everywhere else in the world, like in Mexico, Canada, ect.
Grams and Kilograms are the units of measuring mass of an object.
ADDED: The only legal units of measure for commerce in Britain now are metric, with very few exceptions. You cannot buy so-many pounds of potatoes in the UK - they have to be sold in kilogrammes (to use the correct spelling of this French word!).