Creating Sounds in GarageBand

Create New Project.

Name your project.

Go to Track>New Track.
Select Real Instrument.

Select Vocals and pick your vocal style.

Plug in microphone and select "yes" when you are asked if you want to use C-Media USB Audio Device.

Check input source and adjust recording level.

Click on the track you want to record and click the red record butting when you want to start recording.

To share your sound so you can use it in Flash or other programs:

Make sure you remember exactly where you save your file.