I have an apple mac with inbuilt microphone, but I'm not being heard during the exercises. What to do?
Turn up the input volume as high as you can--that made the largest difference for me. Also experiment with the placement of your mic, which might mean adjusting your monitor or leaning closer to the mic when you speak.
If that seems to have no effect, it might help to do some troubleshooting of flash: I've found that my flash settings tend to interfere when I don't expect them to.
Also, if you change the title of your post to something descriptive, like "mic not picking up sound," you will get more responses. People who spam the forums asking for lingots or trying to find their friends tend to use their names as subject lines. :/