Sometimes a decimal is too small or too large, At this memont write it using scientific notation is easier. For example The speed of light is 299792458 m/s, It could be written like 2.99792458×108 ≈ 3×108 m/s in scientific notation.
To number 0.01234 would be written as 1.234 x 10^-2 in scientific notation.
Decimal to Scientific Notation Conversion is made easier here.