When we conduct an experiment, there are independent, dependent and controlled variables. An independent variable is the parameter that is changed by the experimenter, while the dependent variable is the parameter that changes as a result and is measured by the experimenter. The controlled variable is the parameter that is controlled by the experimenter.
In the germinating bean experiment, one can vary different parameters to study the effect of variations in them (one at a time) on the germination of the seeds. The independent variables in this experiment can be soil (type and quantity), water (amount and interval of watering), or sunlight (absence or presence), among others. For each of these independent variables, the dependent variable is the germination of seeds. Thus, for the experiment, we can vary one variable at a time, say one pot (containing the bean seeds in the soil) is kept out in the sun, while the other is kept in the dark. Each day, we can observe if the seeds have germinated or not, and if they have, how many.
One can also study the length that the bean plants grow as the dependent variable for each of these independent variables.
Hope this helps.