How can I create signal interference in a circuit?
You need to add these two voltage signals.
There's many ways of doing that, for example using an opamp in summing amplifier configuration.

I assume I would need to use two functions generators, how would they need to be set up?

Well, you don't need a function generator to generate an oscillation. Any oscillator does that, and there's hundreds of different oscillator circuits.
Realistically, you seem to be looking for a demonstration: Your sound card has two channels, can be instructed to produce arbitrary signals (aside from constant values, typically) up to some 20 kHz or so.