The Circuit Scribe makes it possible to sketch circuits on paper and use them directly. Below you can see some expert modules to extend your kits. In addition there are basic modules.
Check out these modules and their functions:
Photo Sensor

The photo transistor is used to build circuits that react to light. The more light on the sensor means the more output. For instance, if you set a buzzer behind it, it will give a signal as soon as it's bright enough.

Potentiometer

The potentiometer works like an adjustable resistor, so it's like many resistors in one device. Set the output with the turning knob to regulate how much voltage goes to the following modules, for example to change the brightness of a lamp.