i have a mac book pro - on Skype i can not be heard

Have you set up the preferences in Skype to use the correct microphone, it is under the Audio/Video preference tab in Skype.

Also check that you are using the correct Microphone setting in the Mac system/preferences.

You can't hear other callers:

Why can't I hear the other person in Skype for Mac OS X?

Other callers can't hear you:

Why can’t my friend hear me on Skype for Mac OS X?