Many multimedia programs require libraries and/or drivers in order to function properly. The packages in this section fall into this category. Generally you only need to install these if you are installing a program which has the library listed as either a requirement, or as an option to enable it to support certain functionality.
The first question which people tend to ask about ALSA is why they should use it over the sound drivers included in the kernel—there are several reasons. First, the ALSA drivers support more sound cards than those in the kernel. Second, the OSS emulation is in some cases faster and better than the original OSS driver itself. And finally, there are some programs which can use ALSA's enhanced features to better drive the sound card.
ALSA is also the future of Linux Sound (hence the name Advanced Linux Sound Architecture). The ALSA drivers were included into the main Linux kernel during the 2.5 development series, and they are now the "standard" sound drivers in the 2.6 stable kernel.
The following six sections of the book deal with the six separate components of ALSA: the drivers, the libraries, the utilities, the tools, the firmware and the OSS compatibility libraries.