How to download and install a codec pack, like K-Lite Codec Pack for Windows, for Ubuntu 13.04 and from where? I'm new to Ubuntu and not a developer.
You can install the ubuntu-restricted-extras package either by searching for it in the Software Centre or by running the command...
sudo apt-get install ubuntu-restricted-extras
This package contains a lot of the codecs you would usually need. Also if you try playing a media file that you don't have the codec for then you should get asked if you want to download it automatically.
Another option is to install VLC to play your media files, this doesn't need any extra codec packages installed as they are already built into the player itself.
On Ubuntu exist different multimedia frameworks/libraries with a different codec systems. The default applications on Ubuntu all use gstreamer. Codecs for gstreamer are implemented as plugins and can be found in software center (or synaptic, which is probably easier to use for technical packages) under the name gstreamer-plugins-(something).
Other often encountered multimedia libraries or -interfaces (calling them frameworks would probably be exaggerated) apart from gstreamer are offered by xine, ffmpeg, vlc, mplayer,... which all make use of libavcodec and therefore can handle nearly all widely used audio- and video encodings without the need for any additional codecs.
In addition to these, many codecs are available as shared libraries, that might be used by programs. Examples are xvid or x264. Usually these libraries are linked at compile time, so they will be installed automatically as a dependecy, when a program is installed that uses them. Most of these codecs are not required for playback, since libavcodec can handle files created with them (and at least in the case of xvid is also faster). They can be required or give advantages for encoding.
If you are looking for a powerful encoder, have a look at ffmpeg and mencoder - both support a wide variety of codecs. The mencoder documentation is a good starting point for anyone working with video, since it gives many often ignored but important details about MPEG codecs that help to achieve good quality.