Some problems about the decompiled LUA codes

I decompiled some of the LUA files of Mafia2.

But I couldn’t understand them.

For example :

I noticed that each LUA file has these two functions:

function
onGameInit(_ARG_0_
)

xxxxxxx

end

 

function
onEvent(_ARG_0_
,
_ARG_1_
)

xxxxxxx

end

1. Is the function “onGameInit” the main function, or the function “onEvent”?

2. What do the _ARG_0_
and
_ARG_1_
mean?