This is how yammi looks like in action:
The general usage of Yammi is intuitive:
On the left, the "Quick Browser" provides a list of folders, each containing a list of songs or subfolders.
On the right, all songs contained in the currently selected folder are shown.
Normally you would use the Quick Browser to pick a selection of (or all) songs, then the songlist to pick one (or more) songs to play, edit, categorise, ...
Alternatively, you can type something into the search field to search for a particular song, artist or album.
The most important actions are available in the toolbar or context-menu (right-click on a song or a folder), the rest is available via the main menu.