The above design requires four subforms. Each subform should be based on the junction table with book id as the link child and master field and a combo box based on the relevant table for the second table id.
For example, your first subform is Authors, the table it is based on is Libri_Autori
Link Master Field: Id
Link Child Field: SchedaLibro
Combobox:
Control Source: SchedaAutore
Row Source : SELECT Id, Nome FROM Autori
Bound Column: 1
Column Count : 2
Column Widths : 0, 2
Create your book form and then start adding subforms, the wizards will do most of the work for you.
To add records to the authors table, you need to set Limit To List to Yes and run code on the Not In List event. I like to use a small pop-out form to add items to the "back ground" tables. This may be easier with Access 2010, because you can set a ListItemsEditForm
1, The book form, just before adding the subform. Note that Use Control Wizards is selected. This is the default, so unless you unselected it, it should be fine.
![Step 1 Using a wizard](https://i.stack.imgur.com/hkZMx.png)
The various wizard steps for adding a subform
![Wizard steps for adding a subform](https://i.stack.imgur.com/zJcuI.jpg)
Selecting the subform fields
![Selecting the subform fields](https://i.stack.imgur.com/3zDn1.jpg)
Selecting the link child and master fields
![Selecting the link child and master fields](https://i.stack.imgur.com/dnYQp.jpg)
The form showing the subform control highlighted in yellow and the control properties
![Subfrom control](https://i.stack.imgur.com/vLjuT.png)
2, Adding the combo
You can either change the field added by the subform wizard to a combo by right clicking and setting the properties yourself ...
![Right-click for change to combo](https://i.stack.imgur.com/GHUDk.png)
... or you can delete the existing control and add a combo using the wizard. The first step is to choose the type of combo.
![Step 1 combo type](https://i.stack.imgur.com/ZeS7Z.jpg)
The second step is to choose the table or query
![Step 2 choose table or query](https://i.stack.imgur.com/UmN81.jpg)
Step three is to choose the fields
![Step 3 choose fields](https://i.stack.imgur.com/eJ8CV.jpg)
Step four chooses the sort order and is not displayed here, this is step five, which is to set the column widths
![Step 4 skipped, step 5 set column widths](https://i.stack.imgur.com/LPXy9.jpg)
Step six is to set the Control Source
![Step 6 set Control Source](https://i.stack.imgur.com/2Htb8.jpg)
You will end up with a combobox with the properties illustrated
![Subform combo and properties](https://i.stack.imgur.com/wkkGL.png)
Final form
![Final form](https://i.stack.imgur.com/6TDra.png)