For example:
The producers are plants so you could say that you saw a bush or grass, the primary consumer is a insect maybe a grass hopper and then you saw a snake that ate the grass hopper thats the secondary consumer. After a while you found the snake dead and its corpse is decayed and is decomposed by bacteria... thats your decomposer. How energy is transferred. 1) plants use photosynthesis by sunlight 2) the consumer gets some of that energy when they feed on the producer (or any other consumers) and the rest may be wasted as heat.