In our tests, we just plugged in the USB microphone and it was automatically recognised and was ready for use.Go to Settings > Advanced Settings > Privacy > Content Settings and check that the microphone can be accessed.
Type Speech into Find a Setting, choose Speech Recognition and then Set up Microphone.
Plug in your microphone and check that it is set up and working: We recommend using a good USB microphone, such as the Andrea NC 181VM microphone (£29.95 from Iansyst). Your computer may have a built-in microphone, but you usually get better results with an external microphone.