Well, it doesn't help that the word ideology is being used in different ways. In non-Marxist contexts, an ideology is a political theory: liberalism, socialism, fascism, etc. When Zizek uses the word, it is in the traditional Marxist sense of the beliefs and ideas that sustain capitalism, especially that persuade the working class to support capitalism. An ideological statement would be something like "rising tides lift all boats" to support cutting taxes for the rich.
Zizek uses the metaphor of parallax to explain ideology. Parallax is the phenomenon where a distant object's position seems to shift depending on the position of the viewer. Two people looking at the same object from different angles will see something different. Zizek's point is that this isn't an epistemic problem where one person is wrong (lying, deluded, etc.) and the other is right. The conflict is ontological—the parallax shift is part of reality itself.
The true ideological move is to claim that you've stepped back from the conflicting perspectives to a neutral, objective standpoint, some kind of middle ground where all differences are reconciled. This move is always epistemic, i.e. "Both sides have good points, but they're blinded by their beliefs and can't see how things really are." The truth is not a middle position halfway between two people who are looking out at a distant object and seeing different things due to parallax.
Zizek says the They Live glasses are like critique-of-ideology glasses, not because they show the that the "true" meaning behind advertising is "Obey", "Consume", etc. It's because they render the conflict visible. Ultimately, one is forced to pick a side-which is a political choice-because there is no neutral objective position.