I had trouble learning this, but I'll give you my best answer.
Lets use 0.0000084 and turn it into 8.4 × 10^-6
First, move the decimal place until you have a number between 1 and 10. If you keep moving the decimal point to the right in 0.0000084 you will get 8.4.
Next, count how many places you moved the decimal point. You had to move it 6 places to the right to change 0.0000084 to 8.4. You can show that you moved it 6 places to the right by noting that the number should be multiplied by 10^-6.
8.4 * 10^-6= 0.0000084. I hope this helped.
