Step 1: open maps engine admin console. Select "Layers" followed by the layer you want to work on.
Step 2: With the Layer open the "Edit layer style" menu item becomes available, click it.
Step 3: Layer style editor opens, by default all zoom levels are covered by one style, to add different styles click the "Add Rule" button.
Step 4: the "Add Rule" button brings up an additional options box, set the zoom using the slider and whatever style is defined is used when the zoom matched the slider.
Step 5: Once you are happy with your settings click "Apply"
In the last two images the line feature is red at zoom levels 4 to 9 and green from 11 to 24.
TRAP FOR YOUNG PLAYERS.
In the example above teh line feature is NOT visible in layers 1,2,3 or 10 because no rule exists for these layers, this may be useful for eliminating clutter at zooms like all of Australia (or where ever).
Happy Mapping and if anything is unclear leave a comment.