How can I add an application to the Favourites in the Applications menu?
There are two ways to do this.
Go to 'Activities Overview' in the 'Applications' menu (or press the super key), then either 'show applications' and find the application you want, or search for it in the provided box, then right click and 'Add to Favourites'.
Or if the application is already running, you can right click the application's icon in the Dash in the Activities Overview and select Add to Favourites