You have the OLD model and will not be like the other op's 06.
You just push the start button. Do NOT crank more than 15 to 20 seconds as you may burn out the starter IF you have a starter. Please post the Model number and spec of your Onan. I do not know when Onan went to having starters. The older models used the Main Armature as the starter. IF the unit has NOT been used in years, then the Carb and fuel pump are probably gummed up. Also, that old a unit may have rotted rubber fuel lines from the Main gas tank to the Onan. You also have to have at least 1/3 tank of fuel as the Onan stops pulling Gas from the fuel tank at the 1/4 level. The indicator light will not come on until the Onan is running on the older models. Doug