Nice answer gary, but you didnt actually answer the question lol 'how' to start the engines.

Basically Cpt farham follow garymbuskas instructions, you need to set up a saved flight with everything shut down because by default it always starts all engines running. If your not sure how to stop the engines it is ctrl shift F1 then turn off avionics and battery.
Save the flight like gary says at any regular airport. Then when you start there merely load that flight.
Turn on battery and avionics and press ctrl E to start engines and your away. If you land at an airport and wish to fly back the next day (say) shut everything down and save it again.
I fly for a VA and have a saved flight for the aircraft, so wherever I am I save the flight, then next time I fly I start from where I left off, fuel and everything.