Take a couple of minutes to watch the Toolbar Editing tutorial video (it doesn't need any sound):
[Toolbar Editing (video tutorial))
It will give you a rough idea of how creating buttons in Opus works, from simple pre-made buttons to more complex command-based ones.
A couple of things that are not shown in the tutorial are that you can drag any button to the desktop to create something you can double-click on from there, and you can also have floating and/or docked toolbars which are independent of listers. The docked ones stick to the side of the screen much like the Windows Taskbar. These are great for launching applications and Opus commands alike. The big win is the ease with which you can customize things: You can have some buttons, some menus, some hotkeys, or a mixture of them all. Buttons can launch up to three different things depending on which mouse button you click on which helps to save space and group related commands and tools. Hotkeys can be system-wide if you like, in which case they will work even when Opus isn't the active program. That sort of thing...