From the manual:
Main MenuBy pressing the ESC key you go to the Main Menu at any point within the game.
The various items on the menu are explained individually here:
Return to gameThis option returns you to the current gamebeing played.
Save gameWhen this option is chosen, the game automatically creates a new game status. Once the game has been saved successfully, the option is shown in gray. Please note that the game cannot be saved during a dialog or video sequence.
Load gameClicking on this menu item takes you to the screen where saved games are displayed. Each of those games is represented by a picture showing the game status when that game was last saved. To continue a saved game, all you need to do is to click on the corresponding picture. The progress of a game you might have been playing just before this will be discarded thereby. If you have created a status for more than 12 games, you can use the arrows in the lower right or left corner of the screen to display games with an older status.
To return to the Main Menu, click on the corresponding option in the middle of the lower edge of the screen.
New GameThis option starts a new game. Please make sure that you have saved the game you are currently playing, because progress that has not been saved will be discarded.
Exit to WindowsThis option takes you back to the Windows desktop without saving a game.
Effects VolumeThis option sets the volume for the sound effects. The volumes for music and spoken language output
are set separately.
VoiceThe volume for spoken language can be adjusted here.
SubtitlesThis option defines whether subtitles are to be shown during the game when dialogs occur.
Anti AliasingWhen “Anti Aliasing” is activated the picture looks softer. This option should remain activated as long as game play continues to run smoothly.
CONTROLS:Moving Mona and carrying out actions:Clicking with the left mouse button (LMB) on any point chosen on the screen moves Mona as close as possible to that point. If an object or character is located on that spot, holding the LMB down calls up a menu that allows 4 actions to be carried out. Those actions are: examine object, use/pick up, talk, and fly to the object in the shape of a bat. The exact action that Mona can carry out will be different depending on the game context involved. This will be shown to you by holding the cursor over the various actions.
InventoryEach object you have gathered up is kept in the inventory. You can view them at any time by pressing down the right mouse button (RMB). Just the same as described above for objects located in the surroundings, Mona can carry out 4 actions with things in the inventory. Mona can try to combine an object from the inventory with any other object or character, both in the inventory or in the surroundings, via a brief click using the LMB on the mouse. To combine 2 objects from the inventory, simply connect the item to your mouse button by clicking the LMB, and then move it over the item you want to combine with, and click the LMB again. To use an object from the inventory together with an object from the surroundings, first click on the object in the inventory, then leave the inventory by moving the mouse cursor to the edge of the screen, and then click on the object that is supposed to be used together with the first one. Once again: To leave the inventory, just move the cursor to any edge of the screen.
Conversations:A conversation can be started by moving the cursor to a character; then keep the left-hand button pressed down and choose the “Talk to” action. Frequently you can choose between different questions or replies. Various options are shown in the lower part of the screen so that you can do this. You can select the option you want with a left-click. A question that you’ve already heard the answer to is greyed out, so you always know what questions are still left to ask. If there is more than a handful of talking points available, a scroll icon will appear on the lower right side of the screen.
Exits:If the mouse cursor on the screen turns into an arrow, this means it is showing you an exit into another scene or the picture will be cropped differently. Here, a RMB click enables you to jump directly to a different scene without having to wait for Mona to reach the spot that was clicked on.
To sum things up once again:
Brief LMB click: go to a place, pick up object from the inventory, combine object from the inventory with object/person, choose conversation option.
Longer left-hand click: open action menu.
Right-hand click: open inventory, jump to scene referred to.
If you don't have the manual and would like to see it, you can find it online
HERE.