The Earth is about 149,600,000 km from the Sun. Which is this distance in standard form?

Put the decimal point after the first digit to get 1.496, then count the places it moved: 8. So the distance is $1.496\times 10^8$ km. $14.96\times 10^7$ has the right value but is not standard form, because standard form needs exactly one non-zero digit before the decimal point.