Plug in your audio interface or USB microphone into the computer. If you are using an audio interface, plug the microphone into the first input. Open Acid Pro. It should recognize your interface or microphone as the input, but if it does not, change the device drivers settings in "Preferences" in the "File" menu.
Create a new track. To enable recording for that track select the "Arm to Record" button in the track list. The button is red and round and will blink when properly armed.
Click the "Record" button to begin recording. The record button is located on the playback strip at the bottom of the program. It is a round button with a red circle in the middle. It will light up once it is ready to record your vocals.
Click the "Record" button again when you are finished recording your vocal track. Select "Save as" from the file menu, or hit the "Delete" button on your keyboard to get rid of the track and start over.