Not sure of getting your question, but here we go.
An ecosystem stocks matter and energy inside of living organisms.
As an ecosystem grows, the inorganic matter gets into the ecosystem and can become organic matter. This transformation is called primary production and is realised by vegetals using photosynthesis, some chimiosynthetic bacterias in deep-sea ecosystem etc ...
The productivity of an ecosystem is function of its stage. If an ecosystem is growing (like a field growing out to be a forest), the productivity would be high. A young forest is more productive than a mature one which doesn't grow anymore.
Hope it helps you :)
Gross primary production is the amount producers create over a set period of time whereas net primary productivity is former once respiration has been accounted for.
Gross primary production (GPP) is the rate at which primary producers convert energy to chemical biomass.
If you subtract the amount of energy the primary producer uses for respiration, you have the net primary production (NPP).
Much of the energy from GPP is used by the producer for cellular respiration. What energy is leftover, the NPP, is potentially available for other organisms to consume.