@Mr.Rent
I'm not sure if I understand you but I at first thought the icon on the bottom right was for adding files/directories to the library which it isn't for. It just adds files to your current playlist circumventing the library.
To add files to your library click the title bar and then "Manage library".
This probably only works if your files are tagged.
The meaning of all the buttons is explained in a help screen a button to which can be found at the bottom of the about screen.

@somebody
Some flac albums (not singlefile+cue) pause after each track (these are probably the same where tracks can't be seeked).