You can see the new buttons added after the separator in the toolbar.
Froala WYSIWYG HTML Editor covers a lot of functionalities through the default buttons. However, you might need buttons with another behavior to be integrated in the toolbar. This can be done by defining a custom command and then passing the command in the buttons list. More details about defining a custom command can be found in the Custom Button concept.
After defining custom buttons you need to add them to the toolbar buttons list, using the following options: toolbarButtons, toolbarButtonsMD, toolbarButtonsSM and toolbarButtonsXS as explained in the Custom Toolbar example.