Independent is the variable being changed.

Dependent is what you are measuring.

Controlled are the variables you aren't changing to ensure it is a fair test.

Example:

You are trying to find out what flower grows the tallest. You're going to be using a sunflower, daisy and rose.

The independent variable is the type of flower since that is what you are changing.

The dependent variable is the height of the plant. That's what you are measuring.

To keep it a fair test, you need to keep the amount of water given to each plant, the amount of sunlight, type of soil (and more) the same. These are all controlled variables.