Open your preferred digital audio workstation, or "DAW." Double-click on the desktop icon. Some DAW, such as Logic, automatically open the last saved session; others open a blank session. In cases where the relevant session doesn't open right away, click "File" and select "Open Recent."
Hit "Play" so you can hear the audio in real time. Starting with the first audio channel, click the "Solo" button -- marked by a red "S" icon next to the gain slider dial -- to identify which instruments are recorded to which track. When you come across a vocal track, double-click "Audio" and rename the track. Use names that are meaningful to avoid confusion -- "Lead Vox Take 1," for example. Pressing the Solo button again will restore audio to the muted channels.
Click "File" and select "New Audio." Name the audio track "Vocal Sub Mix." Click on "Vocal Sub Mix" and select "Send To." Select "Stereo Bus."
Click "Send To" on each of the vocal tracks and select "Vocal Sub Mix." This configures the interface so that each vocal is grouped on one stereo track.
Click on "Vocal Sub Mix" and select "Export as WAV." This renders the grouped vocals as one audio file. WAV is a preferred format because it is doesn't compress the audio like an MP3 does.
Click "File" and select "Open New."
Name the session "Vocals Only" when prompted.
Click "File" and select "New Audio." This opens a single audio channel. Name the channel "Vocals."
Click "File" and select "Import Audio." Browse for "Vocal Sub Mix" and click on it when located. This imports the grouped audio file into the single audio channel. The vocals are now separate from the remainder of the song. From here you can edit them, set them over different songs, slow them down, speed them up and perform myriad other functions with them.