To add the archive widget on your website, go to the WordPress widgets management page via Appearance -> Widgets in your WordPress menu bar.
This page is well-known by the users of WordPress to add a widget to their website.
You will find a new widget called : AcyMailing : Newsletters archive. Drag it to the wanted sidebar to add it where you want.
You can customize the title of the widget and the number of newsletter you want to display.
The widget will appear in the sidebar you have set. It will display the number of newsletter defined in options.
By clicking on an email subject, the email appear in a popup.