You need three thing to start the engine on the A320:
- Make sure you have sufficient air pressure available (eg APU bleed)
- Put the engine mode selector to IGNITION / START position (the switch below the engine master switches)
- Then, once the amber crosses on the engine display have disappeared, the engine master switch is put to ON. This opens the start valve and the engine starts up. Now all you do is monitor the engines' parameters and, when both engines are running, the mode selector is set into the NORM position.