Audacity basic questions

An Audacity neophyte here. I opened an MP3 file in Audacity (on my iMac). It plays, no problem. I want to copy a portion of the file out as a separate file to be able to burn it to a CD or bring into iTunes as an independent tune.

The commands under Edit that seem like they are appropriate to do that are "greyed out". What am I doing wrong?

Thanks for your help.