Answer:
The independent variable is the cause. Its value is independent of other variables in your study.
The dependent variable is the effect. Its value depends on changes in the independent variable.
Example:
You design a study to test whether changes in room temperature have an effect on math test scores.
Your independent variable is the temperature of the room. You vary the room temperature by making it cooler for half the participants, and warmer for the other half.
Your dependent variable is math test scores. You measure the math skills of all participants using a standardized test and check whether they differ based on room temperature.