0.1 = 10⁻¹
And just keep going.
0.01 = 10⁻²
0.001 =10⁻³
0.001 = 10⁻⁴…
We can take this as far as we want.
We can now take any large or small number and reduce it to the first few digits — depending on how accurate we need it to be — an multiply it by 10 to an exponent derived from counting how far, and in which direction, we needed to move the decimal point to get it behind the first non-zero digit.
The Sun is 1.5 • 10¹¹ meters away. An Electron has a classical radius of 2.818 • 10⁻¹⁵ meters. The formating on Yahoo answers doesn't make this easy to do as you've noted. There are several other notations that can be used rather than the superscript. The more common its the caret: ^ to denote superscript; e.g., 10^19 for 10¹⁹. A second is "E" for exponent as used by many calculators; e.g.,10E-15 for 10⁻¹⁵.
As an added bonus, scientific notation makes multiplication and division almost as easy as addition and subtraction.