To record your voice,
1. Launch QuickTime player from LaunchPad.
2. Select File -> New Audio Recording
3. Click the Record button (Red circle) to start recording your voice.
4. I am using MacBook Pro with Retina Display and in this Mac I don't need an external microphone to record my voice. Mac has an inbuilt microphone doing the job for you
5. It is also smart enough to minimise the noise and distortions around you.
6. Once you complete recording, click on the Stop button (Green square button).
7. Go to File -> Save and save the file at your desired location.