Scientific notation is used to express very large or very small numbers conveniently. It allows easy comparison between numbers that would otherwise require counting zeroes. Take for example 1000000 and 10000000. To determine which of these numbers is larger, you need to count each zeroes, and this process could prove to be more tedious, not to mention that it is also prone to errors. However, when written in scientific notation in the form a x 10n: 1000000 can be expressed as 1 x 106 whereas 10000000 can be expressed as 1 x 107. These expressions were arrived at by determining the numerical factor a, which is a number between 1 and 10 that can be drawn from the given number, and n, which is the number of places that the decimal point was moved (n is positive when the decimal point was moved to the left, otherwise, it's negative). Since both these numbers have positive exponents in 10, then comparing them would be easy--the greater the number of n, the larger the number. Thus, 1x107 is larger than 1x106.
I hope this helps.