Point your microphone in the general direction of your speakers and ensure that Mic is selected.  Uncheck the input Mute, and then uncheck the output Mute.  You may have to adjust the input and output sliders or move the mike but you should get something like this pic.  Don't worry if the yellow trace jumps about a bit.  The stability of the input is a function of your soundboard and PC's performance, and how noisy it is where you are.

Turn the speakers off using the output slider and then whistle at the mike.  You've got an oscilloscope!  (Intriguing, isn't it, that a whistle is a pretty good sine wave.)

Set Frequency 1 (Hz) to 100 Hz, set the Sweep check Frequency 2 (Hz) to 600 Hz, and Duration (s) to 2.5 seconds.  Now use the output slider to turn the speakers up et voila a frequency response.  Not bad for a cheapo mike!