I downloaded a RAR file which has FLAC and CUE files. The flac file seems to include all tracks from the original cd combined.
How can I reconstruct and burn the original CD ?

It appears that the FLAC file is a CD image, you can use Burrrn and the cue file to burn a copy of the original CD. Simply open Burrrn and drag n' drop the cuesheet onto it, the names of the songs should appear in the correct order and then you burn the CD.