Six million four hundred and five is 6,000,405. The place values from left to right are ones, tens, hundreds, thousands, ten thousands, hundred thousands, millions. Thus there are 6 millions, no hundred thousands, no ten thousands, no thousands, 4 hundreds, no tens and 5 ones.
Note that Britain and the US (and strangely most of the scientific community) disagree about higher place values like billions, but agree up to the hundred millions. In Great Britain, a billion has twice as many zeros as a million so has 12 zeros, and a trillion has 3 times as many zeros or 18 zeros. While in the US a billion has 9 zeros and a trillion has 12 zeros.