Libertine Fonts are provided as tgz-archives. Windows-/Mac-users may need a proper software such as 7-Zip for uncompression.
Files with “Font” in file name contain the fonts in OTF- and TTF-format. Files with “SRC” in the file name contain the Fontforge source files
Windows: Copy fonts into folder C:\windows\fonts.
Linux: Use system programs such as KDE-Kontrol to install the fonts. These also update Linux specific system files.