Scientific notation is used to express very large and very small numbers in a way that makes them easier to work with. It writes a number as the product of a coefficient and a power of 10, where the coefficient is between 1 and 10 and the exponent indicates how many places the decimal is moved. Examples show how scientific notation can be used to write the mass of a gold atom or the number of hydrogen atoms in a gram of hydrogen in a more manageable way. The document then provides steps for converting a number to scientific notation and examples of performing this conversion.