Hi! When you’re in the game, in the top right corner of the text box, there should be a couple of different words listed (e.g., Load, Stats, History, etc.). Each of these, when clicked, should allow you to execute the corresponding action.
The word “Save” should be in that area, and you should be able to access the Save Menu from there! Alternatively, Renpy (the software used to make the game) automatically assigns the Save Menu function to the right click on your mouse. So you can also right click to access the Save Menu and save the game! Let us know if you continue to experience issues/ need more explanation!