In the picture above, you can see one example of a food web in my ecosystem. The initial energy comes form the sun in the form of light energy. The plants take this light energy and turn it into glucose which is a form of stored energy through photosynthesis. When the animals eat these plants, they gain the stored energy from the plants. Then, through cellular respiration, they turn the stored energy into heat and movement energy.
Here's an example of a general energy pyramid that demonstrates the 10% energy rule. The rule states that only 10% of the energy is passed on to the next level.
Image Source: https://en.wikipedia.org/wiki/Ecological_pyramid