i use the AMD 4 and the mathematica 10.0 student edition

Works on my system (OS X, Yosemite). I have read that the function is a bit flakey on Windows or Linux. Perhaps someone with experience on those systems can help -- assuming that you are not on a Mac.

I did that but it keeps showing me an error message. Am confused...

You need to provide more information. You can record sound, but not continuously, and the mechanism is platform dependent.

SystemDialogInput["RecordSound"]

will open a dialog on your system. You record the audio, and assign it to a variable. You can then process it.

What you cannot do is continuously sample the microphone. If you can figure out how to do this, let all of us know.