A negative exponent means that you have a fraction whose numerator is 1, and the denominator is raised to the positive power.
For additional explanation about laws of exponents, especially NEGATIVE EXPONENTS, please see my website by clicking on my tutor name "rapaljer" anywhere in algebra.com. Look for my second link, which is "Basic, Intermediate, and College Algebra: One Step at a Time". Click on "Basic Algebra", look for Chapter 2, Section 2.13 Laws of Exponents: Zero and Negative Exponents. These explanations are written for students who have trouble with math concepts.