Howto:Start the main engine

When you've spawned as an engineer, the first thing you should do is open the engine blast door at the top left of the engine control room, by clicking on the remote door control. Then go to the plasma storage room, which is immediately to the right of the engine room, and start bringing back 02 and plasma into the engine itself. Pack it with about 10-15 plasma containers, and an equal measure of 02 containers, then go down to the engine igniter (it's to the bottom of the engine itself), open the grill with wire cutters, and turn off the air-siphons. 
Then go back into the control room, close the blast door, then attach a plasma container to the second connecter, below the first one which starts spawned and connected. Connect the second plasma container with a wrench, then set both of them to the maximum pipe release, and open the valve they are both connected to.
Then go down to the 02 connecter next to the igniter, and connect it with a wrench, then set it to maximum release. The engine should ignite shortly.
After it has ignited, close the ignition blast doors, for higher engine efficiency 
Drag the two c02 canisters to the generator room (the one with the large white generator in the middle, to the north west of the engine room. Swap the empty c02 canisters for the fresh ones, and set them to full pipe release once you have connected them with a wrench.
Go to the generator, and set the hot/cold loops to on, then set the cold loop to 1% and the hot loop to 100%. 
Then go to the power cells on your right, and set them to auto-charging, and the input to 200k and the output to 80k or so. This should charge them fast enough and get a steady supply of power to the station. Once they have started charging remember to set each output to online.
If you run out of c02, connect an empty canister to the pipe that leads to the inlet in the engine, and set it to pipe accept, and open the valve, and it will refill it. 
Congratulations, if you've done this right, you should be making about a megawatt of power and the crew won't be baying for your blood for not getting the station powered up.
If you use all the plasma from the storage, you can make about 3 megawatts, but that wastes power, as the cells can only accept 600 kilowatts.