Read the game_save description in the manual:
game_save(STRING* name,var number,var mode)
Saves the current state of the application in a .sav file the savedir folder, for later resuming the game at the current position.
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Remarks:
Objects are stored by their indices. Therefore levels, scripts, and objects must not change between game_save and game_load, with exception of level entities. All .._create and .._remove functions, except for creating and removing level entities, must be executed before the first game_save or game_load call.
Hope this helps.