I will make this interesting. There is an autostart feauture in most commercial planes, but in order to accurately describe what occurs, lets say we are going to start the engines manually. Provided you have completed your pre-flights and everything else is configured, heres what happens. On a large jet, you will need to turn off all but one of the packs, so the APU's air will be directed to the turbofans instead of other sources. (this ensures an easier start up) The ignition is then turned on, which yes, provides sparks to ignite the fuel just like a car does. Heres where things get a little different. With the throttles at idle, and the fuel pumps OFF, you then bleed air from the APU across the fans to start them in motion. There is screen in the cockpit which tells you the percentage of N2 in the turbines. When this percentage reaches between 10-15 (varies by jet) you then turn on the fuel pumps. Fuel is now being introduced into the spinning engine which is full of compressed air and sparks from the ignition. At this point, the result is obvious - compressed air, sparks, rolling turbines, + fuel. The engine will briefly power up for a second then die to idle thrust. You are now ready to taxi.