For me, the following metaphor really helps to envision the relationship between levels and their interactions. Imagine a clear rectangular container viewed from the side. Inside the container are various substances with various degrees of attraction to and repulsion from one another, such as sand, water, vegetable oil, alcohol, pebbles, ice, motor oil, etc. Depending on how they are layered one on top of another the whole structure may be more or less stable, with various fluids in suspension over others, and liquids permeating the solid levels, other liquids flowing together in semi-turbulent fashion, and still others diffusing together in a saturated, even mix. Now imagine laying down a structure from the bottom up where the various levels are generally in suspension, and not co-mingling too much (e.g. sand goes on top of pebbles, oil on top of sand, water on top of oil, etc). Now imagine vibrating the structure horizontally at varying frequencies. One thing you will notice is that for a given frequency each level exhibits more or less stability. Sometimes the agents within a level (e.g. sand grain, water molecule) will react quite dynamically, moving and bumping into one another, fracturing a crystalline structure (e.g. ice) and other “highly entropic” behavior. Other times the agents within the level (and hence the level itself) will remain quite stable in the midst of the chaos ensuing above or below it. Still other times, two levels will interact in complex ways, mingling, avalanching, flowing turbulently, flowing in a laminar fashion, with entire levels decomposing and fusing with other levels. Interactions can even take place between levels that are distant, though this happens with less frequency than between levels that share a direct interface.
I should caution you from taking this model too far, since it’s (as always) an oversimplification. For one, in our constructed example, the higher levels did not emerge from lower levels. They were “designed” by us. The interface between designed levels is likely to be much less integrated than that between emergent levels. Still, some of the dynamics observed in designed multi-level systems appear reminiscent of emergent levels.