An exponent is the number in superscript on the right side of the variable. For example, x2, x is the variable and 2 is its exponent. To multiply variables with exponents, all we need to do is the add up the exponents of the SAME VARIABLE, and the sum will become the new exponent. For example:
x6 * x3 = x9
Here, the exponents are 6 and 3. We only have x as variable here, so by adding up 6 and 3 we get 9 as exponent.
What about x6 * x3 * y2?
Since x and y are different variables, we can't add up their exponents. So we only get x9y2.