Apart from a defective microphone, the only reason why the other person could not hear you is, if either
-you pressed Mute in Skype
-the other person has muted their speakers
-temporary glitch
Skype on the iPad is dead simple. There aren't any special settings.
So if the above doesn't fix it, you can still try the universal problem solvers:
Restarting iPad:
restart the iPad by pressing the power button, then slide to power off,
Restarting the app:
Close Skype completely, by pressing the Home button twice, then press &hold on the Skype icon, when it starts wiggling, press on the red x. Now press the home button.
Hopefully this solves the muted sound.