It’s not a toggle switch, just a simple single-throw, single-pole switch (boring old normal switch). Actually, looking back, I can see that the diagram I provided is actually somewhat confusing because of how I placed the switch box. I’m going to try to re-draw that part of the circuit with text, so bear with me.

5V
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Switch
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L___ Digital Input
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Big Resistor
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Ground

When the switch is open, you have a circuit that connects the 5V to nothing, so it goes nowhere, and you have a second circuit that connects the digital input to ground. When the digital input is grounded, it doesn’t detect any input and counts as “off” (well, this depends on your code, actually, but in most cases this is how you do it). When you close the switch, you create a three-point circuit. You have a 5V power connected to two things: first a big resistor and then ground, and second the digital input (which is also a ground). So the 5V has to decide where it’s going to go. The big resistor basically acts as a dam, blocking the power and pushing it into another path if available. Since there is a digital input available, the power goes there instead of straight to ground.

Hope that makes sense.

Thomas