I know this is a few years late, but if I found this question other may as well.
The K-Lite CODEC pack (http://klitedownload.com/Download/) is a collection of CODECs that some people find useful for playing audio and video files.
A CODEC is a bit of software that can CODE and/or DECODE audio and video files. (More information here: http://windows.microsoft.com/en-US/windows7/Codecs-frequently-asked-questions)
Do you need the K-Lite CODEC pack? Well that depends, there are people that swear by them and don't apparently have any problems with them, but I personally feel that the crashes that inevitably come are not worth the hassle. (I am one who tends to push my computer to its limit so if there is a crash that could potentially happen, it probably does.) I am sure not everyone will experience crashes.
My suggestion is to not use a CODEC pack. If you find that there is a media file that you need to play but cannot, that you go to the website of the people who make the CODEC and get it from there as it should be the most up-to-date and there is often support options available on the site if you encounter problems. CODEC packs also tend to install way more stuff than you need greatly increasing the possibility of crashes and potently impacting the performance of your computer. This can be mitigated with a selective install, but then if you knew what to select, then you may as well get the files from the source.
If you have little or no idea what I am talking about then a CODEC pack may be a viable option initially as it may get you through in the short term. Then you can educate yourself as you are able and deal with possible crashes as they occur.