Electronic Circuit SImulator

You can drag any of the circuit elements from the right hand toolbox onto the editing grid to create and experiment with your "electronic" circuit. 

To add a wire, click and drag in the editing area.

To rotate a circuit element, by press the 'r' button on the keyboard. 

There are a lot of circuit elements and analysis techniques that you can learn about in 6.002x: Circuits and Electronics, all of which can be used to get automatic feedback using this online laboritory.