Here's the whole idea in one breath: the same artwork can be read four completely different ways, and each way is just a different set of questions you decide to ask of it. Pick a frame, ask its questions, and the picture starts answering. Pick a different frame and it answers differently — but it's still the same picture.
Start with What You Already Do
Stand in front of any portrait and your first thought is usually "do I like it?" That's a real reaction, and it counts — but it's a door, not a room. It tells us about you, not much about the work. The trouble is most people stop right there, at the door, and never go in. They've got one question and they run out of road.
People who read art for a living got sick of running out of road. So over the last century or so, art teachers and critics built a little kit of different lenses — different angles you can deliberately swing onto the same work so it keeps giving. In the New South Wales art classroom we call that kit the frames, and there are four of them: subjective, structural, cultural and postmodern. None of them is the "right" one. They're four torches pointed at the same statue from four sides.
The Four, in a Sentence Each
The subjective frame asks the heart questions: how does this make me feel, and what was the artist feeling? The structural frame asks the maker's questions: how is it built — the line, the colour, the symbols — and how do those parts carry meaning? The cultural frame asks the world questions: what does this tell us about the time, place and people it came from? And the postmodern frame asks the cheeky questions: is this borrowing or quoting something else, is it being ironic, is it poking the rules of "proper" art?
Notice they don't compete. A good reading of a portrait might use two or three of them at once, stacking up until you've said something genuinely rich instead of "yeah, it's alright." In the toy, click around all four on the one face and feel how the same image opens up four different ways. That stacking — that's the whole game, and the rest of this climb is just learning to play it well.