import song from a cd

Use r-mix if you have X2. Listen any find out where the vocal is in the stereo mix and filter it out. I always use rectangular shape filter but you can try whatever that works for you. Experiment until you get the result. I had filtered out Karaoke VCD tracks where the vocal is panned hard right. I was very happy with the result. Most likely your CD's vocal is panned centered. 

To the OP,

Extracting vocals or any particular instrument from a stereo track is a very complex task. There is no set tool or piece of software that just does it. With the judicious use of filters you may be able to go part the way.

It is more dependent on how the original song was recorded than anything. If the vocals were put exactly in the centre there may be a better chance but the more it is effected by reverb and other processing the less likely you will be 100% successful. Too many TV shows give the impression that you can just flip a switch and magically isolate a sound.

The reality is that it's the range of very esoteric and expensive software that has some chance of doing this.

Plugins like R-Mix which is bundled with X2 will have some chance of doing what you want as the others have said but it by no means a given.

Mixing and mastering a life long learning process, to then extract a single part of that is also a process that takes much understanding and practice. Good luck