FLAC is a file format that is described as being "lossless" - in other words, unlike other compressed file formats such as mp3, there is no loss of any information in the audio stream - resulting in a better quality audio file. However, to accommodate for this incrase in quality, FLAC file sizes will be a lot greater than those of mp3s.
You can play FLAC files on your computer by using the VCL Player, which you can download free from here:
http://www.videolan.org/vlc/
To burn FLAC files onto CDR, I usually convert the FLAC into WAV (another lossless file format which plays in all CD players). To do this I use Xilisoft (
http://www.xilisoft.com/mp3-wav-converter.html).