Please tell me how to make saving game event. I wanna give 3 to 4 slots and option to save game at any time and any where they want.
You have to use “Storage” conditions/actions, when the save condition is fullfiled, save on a file the data you want (player position, health, points, etc.). Finally, when load a state, set the variable’s values from the corresponding in the file.
There is an example in the examples folder, the file is called “leveleditor.gdg” or something like that 
If you want to use 3/4 slots, you need 3/4 files or a file with 3/4 “main values” (in each main value, you set the sub-values for each slots as “sub-events”).