A number in scientific notation consists of a number written like this: 2.0 x 103
The 2.0 is called the mantissa and the rest of it is usually referred to as the power or the factor.
To convert it to standard notation, you need to write 2 then follow it by 3 decimal places (in this case, 3 zeros). That means "2000"
If the number has a negative exponent like 2.0 x 10-3 you need to move the decimal point 3 places to the left. "0.0020".
If you were to write Avogadro's Number 6.02 x 1023 out it would give you a cramp in your hand: 602,000,000,000,000,000,000,000. Notice that the decimal point was moved 23 places to the right.
Don't read the next paragraph if you are still confused.
Notice that the 0 following the 2 remains in the second case, that, you will see later, is important for precision if the number in scientific notation was a measurement. In the first case, that zero following the 2 should (technically) have a bar written above it (like the bar you write over a repeating decimal) to indicate that it is meaningful for the measurement.