The recording controls are located near the top of the window.  These should be the only ones you need to make a simple recording.
Click the Start button, and make a test recording.  As soon as you click the button, a pane showing the sound envelope on the stereo tracks will appear.
When you are done, click the Stop button.
Next: Saving the recording as an MP3.
With Audacity, you can make a recording and convert it to an MP3.