To simulate a diode in forward-bias using QUCS, first, create a new circuit and place a diode. Connect the anode to a positive voltage source and the cathode to ground. Configure the voltage source to exceed the diode's threshold (typically 0.7V for silicon). Run the simulation to observe current flow. For Zener diodes, repeat the process but connect the Zener diode in reverse-bias to analyze breakdown voltage effects. This approach highlights both standard and Zener diode behaviors in different bias conditions.