One kilojoule is equal to 1,000 joules of expended energy. The "kilo" prefix refers to a multiple of 1,000 of whatever unit is being expressed. Hence, 1 kilometer equals 1,000 meters and 1 kilogram equals 1,000 grams. To convert units is a matter of multiplying by a factor of 1,000.
A joule is a unit of energy and is used internationally. According to Universe Today, lifting one apple over a distance of 1 meter requires the expenditure of approximately 1 J of work. Lifting 1,000 apples over the same distance, therefore, calls for the expenditure of 1,000 J, or 1 kilojoule of energy.