All geysers of the same type will output at the same average rate. For natural gas geysers, this averages 100g/s- almost enough for two generators.
When entering the cavern with the geyser, make sure you install an airlock to keep it separated from the rest of your base. Entering from the top is preferable as natural gas sinks below oxygen. Build your pump near the bottom and pipe it out of the cavern. A filter is optional but recommended- piping anything besides natural gas into the generators will damage them.
Build two generators nearby. Make sure there is space around them to handle the necessary infrastructure. Pipe the natural gas into them.
The natural gas generator has two outputs- CO2 and polluted water, which you will need to deal with.
Polluted water will drain out of the machine onto the floor; it doesn't use a pipe. The best way to deal with it is to put the generators on a mesh floor and let it drain there. It's up to you whether you pump it out and use it or drain it into the rest of your base's polluted water. Getting rid of it isn't urgent as the generator doesn't produce very much water- it'll take 20 cycles to fill a single tile.
More importantly, you need to get rid of the CO2. The generator produces a lot of it and must output it via a pipe. If this pipe is missing or blocked, the generator will not run. The simplest way to get rid of the CO2 is to pipe it to a Carbon Skimmer and place an output vent there.
If you do things right, this setup should get you a surplus of about 1000W, with room for expansion by adding fertilizer makers to make more gas.