Hydrothermal vent communities derive chemical energy from the material coming out of the seafloor vents, unlike all other known communities on Earth for which the source of energy is the sun. Most steps for energy transfer and transformation would be similar to those in other communities, with one organism being consumed and digested by another, except for the initial capture of energy which would involve prokaryotes which can grab the energy in the material coming from the vents and incorporate it into themselves. In this, they take the place of the photoautotrophs, such as cyanobacteria and plants, in other communities on Earth.
Work Step by Step
Review earlier material on things like trophic levels and energy transfer: the vent communities would only differ from a forest or some other community based on photosynthesis except in the initial energy capture. From that, it is simple to describe the community as the question asks.