The game uses an automatic save feature: it is not possible to save manually. Please note that there is no icon to indicate that the game is saving!
Automatic saves occur when you change locations (when there is a fade to black between scenes).
Automatic saving also occurs when you modify or add something to your journal: you place a glyph, write a guess about a glyph, etc.
In the pause menu, when you click on ‘Quit’, you can see when the game was last saved.