You must complete the voice training from Microsoft before Hal will understand you. Hal uses the Microsoft Speech system. It does not have it's own speech processor.
Check your microphone settings, eliminate as much background noise (fans, tv/radio, street noise, kids playing, etc.) as possible, use a decent quality microphone and speak clearly and directly as if you're speaking to a 4 year old.
That's the best I can offer at the moment.
Good luck!