From the users guide:
Voice Control lets you control music playback using voice commands. To use Voice Control, you need the Apple EarPods with Remote and Mic, or some other compatible accessory with a microphone.
Note: Voice Control may not be available in all languages.
Use Voice Control: Press and hold the Home button until the Voice Control screen appears and you hear a beep.
For best results:
Speak clearly and naturally.
Pause slightly between commands.
Say only iPod touch commands and names.
For a list of available commands, see Siri and Voice Control on page 45.
Voice Control normally expects you to speak voice commands in the language that’s set for iPod touch (in Settings > General > International > Language). Voice Control settings let you change the language for speaking voice commands. Some languages are available in different dialects or accents.
Change the language or country: Go to Settings > General > International > Voice Control, then tap the language or country.
For more about using Voice Control, including information about using Voice Control in different languages, go to support.apple.com/kb/HT3597.
If you meant VoiceOver see: