The Interface
Composer is a split screen. Your settings are on the left, your product is on the right, and the buttons that save and publish run along the bottom.
You can drag the divider between the two halves if you want more room for one or the other.
The left half
A row of section buttons across the top: Models, Scene, GUI, Logic, Navigation, Dimensions, Personalisation, Scripting. Clicking one changes what the panel below shows.
Sections not included in your plan carry a small badge and a note about which plan they need. They stay visible deliberately, so you can look at what a feature does before deciding whether to pay for it.
Some sections have their own sub-tabs. GUI has six, covering the controls themselves, the layout, the styling, translations, pricing and PDF documents, and each shows a count so you can see at a glance how much you have set up.
The right half
Normally the live 3D view. It updates as you edit, so changing a colour or moving a light shows immediately rather than after a reload.
It swaps to a different view when that is more useful. Working in the GUI section replaces the 3D view with a preview of the options panel itself, at desktop or mobile width, so you can see what you are designing. Working on PDF documents replaces it with a preview of the document.
Editing versus playing
There are two modes, and knowing which you are in explains most surprises.
Edit mode is for building. Every model is visible regardless of the conditions you have set on it, because you need to see the thing you are editing. You can click parts to select them, drag them with the on-screen handles, and hide things temporarily to get at what is behind them.
Play mode, which you enter with the Play button, is your customer's view. Conditions apply, so parts appear and disappear as they should. The options panel behaves as it will on the product page. Prices update. Camera moves fire.
If something looks visible in the editor but not in Play, that is usually correct behaviour rather than a bug: in edit mode you see everything, in Play you see only what the current selection calls for.
Stop returns you to editing.
Moving things by hand
Composer has no gizmo toggle buttons. Instead, clicking into a position, rotation or scale field brings up the matching on-screen handles for that thing, and dragging them writes the numbers back into the field.
It works the other way too. Clicking a part in the 3D view selects it and jumps the panel to its settings.
The buttons along the bottom
Play and Stop switch modes.
Save stores your work in the project. Composer also saves periodically on its own, but pressing Save is worth doing before you step away.
Publish sends the configurator to your linked products, which is the separate deliberate step that makes changes public. See Saving and Publishing.
Examples loads a prepared configuration you can pull apart to see how it was done. A good way to learn a feature you have not used.
Files holds import and export: downloading your scene configuration, downloading a full project file including your editor state, copying the configuration to the clipboard, and loading one back in.
Reset Scene rebuilds the 3D view from scratch, which is the thing to try if the preview gets into a strange state.
There is also a badge showing which plan you are on.
When an edit seems to do nothing
The most common cause is a form error somewhere in the editor. If any field is invalid, Composer will not assemble the configuration, so saving, publishing and the live preview all quietly do nothing.
There is a Fix in UI button showing a count when this happens. Press it and it takes you to the offending field. See Troubleshooting if you get stuck.
A note on browsers
Composer is a desktop tool. It works in any current browser, and it wants a reasonably sized screen because you are looking at a settings panel and a 3D view side by side. Building on a phone is not realistic.