Simple Circuit Simulation tutorial

If you are on Windows I would download a copy of LTspice from Linear Technology. IIRC there is a tutorial in the download. If not it is on their website.

LTspice is very quick to get started with. A major advantage is that the package comes with all of the semiconductor models for the LT parts. Most models are copyright and end up having to download them from the manufacturer. This can be a major source of difficulty for people getting started.

Once you have the software I would start with a very simple circuit like a voltage source in series with a resistor in series with a capacitor. Setup your probes to plot the voltage across the capacitor and the voltage across the resistor. This will enable you to learn the quirks of the tool and hopefully get some instant gratification.

Make a copy of the simple circuit and start to add new elements to the new circuit.

http://www.falstad.com/circuit/

Here is a java applet that allows you to simulate your circuits, I find it very useful, (dont have to make a whole new SPICE simulation.. :P )

You can use Qucs.

There are some tutorials here: http://qucs.sourceforge.net/docs.html

For logics circuits, you can use this great online simulator called Logicly.