Here's how:
Let's say you have a number: 12345.
To convert this to scientific notation, do the following:
(1) Move the decimal to the the left until you have a single number in front:
1.2345
(2) Now multiply by 10 to the power of the number of places you moved the decimal; in this case it would be 4, so you multiply by 10^4 to get:
1.2345 x 10^4
Now for decimal values: 0.000123
To convert to scientific notation, do the following:
(1) Move the decimal to the right until you have a single number in front:
1.23
(2) Now multiply by 10 to the _negative_ power of the number of places you moved the decimal; in this case it would be 4, so you multiply by 10^-4 to get:
1.23 x 10^-4
The scientific notation number and the original number have the exact same value because you're multiplying by powers of 10, which has the effect of moving the decimal. Multiplying by a positive power of 10 moves the decimal to the right, multiplying by a negative power of 10 moves the decimal to the left. (Don't get confused, though ... it's backward when you convert from regular to scientific). this will explain.