Two ways to do it:
First way:
000001 through 999999 is 999999 numbers,
and 000000 makes 1000000 numbers.
Second way:
10 ways to choose the 1st digit, times
10 ways to choose the 1st digit, times
10 ways to choose the 1st digit, times
10 ways to choose the 1st digit, times
10 ways to choose the 1st digit, times
10 ways to choose the 1st digit, times
10×10×10×10×10×10 = 106 = 1000000
Edwin