I recommend install Not Enough Items (NEI) mod with Galacticraft, it has recipes and graphics which show how most of the machines work.
If you have another mod with fluid pipes (for example, BuildCraft or EnderIO or Mekanism), the new machines are pretty simple to operate automatically. Place the machines left to right, with fluid pipes between (and a redstone engine to pump each fluid pipe of course). Each machine has its main input on the left side, and its main output on the right side.
It goes like this:
Water ->
Water Electrolyzer -> Hydrogen ->
Methane Synthesizer -> Methane ->
Gas Liquefier -> Fuel
Each machine needs electricity (power it from the underneath, or in Creative mode you can use an Infinite Battery just to test things out).
Methane Synthesizer also needs either Carbon Fragments in the carbon slot, or Carbon Dioxide gas. For now, the only way to get Carbon Dioxide gas is to use the machine on Mars with an Atmospheric Valve in the slot above the carbon dioxide tank.
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If you
don't have another mod with fluid pipes, then you need to place water buckets in the Water Electrolyzer. In a future version of Galacticraft - probably this weekend - you will use the white oxygen pipes to pipe the hydrogen from Water Electrolyzer to Methane Synthesizer. That's not working yet in Galacticraft 3.0.3.200 or 201, so for now you will have to downgrade to 3.0.2.199 which gives you free hydrogen in the Methane Synthesizer.
Then you can use canisters to move methane from the Methane Synthesizer to the Gas Liquefier, and place empty liquid canisters in the right-hand slots in the Gas Liquefier to fill them with fuel.
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- You can automate all the machines with hoppers, Buildcraft pipes, or ME systems. The machines will automatically put filled or empty canisters into the correct slots.
- If you want, you can use the Mekanism Electrolyzer instead of the GC Water Electrolyzer to make hydrogen - both machines do the same thing, and a Mekanism gas tube carrying hydrogen will connect to the Methane Synthesizer.
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If you find anything is not working, please report (with a screenshot would be great).