Places to put comma in is same when we use arabic numbers only. However we pronounce 123,456 like 十二万三千四百五十六 and sometimes write them down in that or 12万3456 form. 十 means 10, 千 is 1k, 万 is 1k^2 , units after that will be 1k^n . Like K, M, G in SI units.