Open Audacity and click on the Record button (red dot in the upper-left hand corner). You will see your audio being recorded. If no audio records, check the following things:

1. Make sure that your microphone is plugged into your computer correctly.
2. Make sure that the control panel device preference (control panel > sounds and audio devices > audio > sound recording default device) matches the audacity device preference (edit > preferences > audio I/O > recording)

To pause during a recording click the pause button (two blue lines) and NOT the stop button (yellow square)--stopping and then recording will create a new audio track.

When you are completely finished, click the stop button (yellow square). Then save your file (File > Save Project As) just in case. To play back your recording, click the rewind button (purple arrows pointing to the left) and then the play button (green triangle).