To multiply fractions, you just multiply the numerators times the other numerators, and the denominators by the other denominators.
In this example,
1/2 * 1/3 * 1/4
is the same as
(1 * 1 * 1) / (2 * 3 * 4)
Since 1 multiplied by itself is always one, the numerator does not change.
2 * 3 = 6
6 * 4 = 24
The final answer is 1/24.
Hope that helped =)