Audacity is a free audio editing utility that is quickly becoming a poor mans version of Pro Tools. It is filled with many of the most important features in audio recording and comes packed with software extras to further aid creativity. With a little practice you can soon be turning out really good recordings that cost you nothing at all.
Click on the record button to lay down a track. When you are finished, click on the stop button to cease recording.
Highlight the track by clicking and dragging, or rewind to the beginning, and hit edit -> select -> cursor to end. This will select the entire track.
Use the DB slider at the left edge of the screen to control volume. A greater DB level means more sound, and a smaller DB level means a quieter track. Dont be afraid to put the DB slider into the negatives. This simply means that you are diminishing the volume level of the original track. There is also an alternate way to affect volume, that should be used if you want to go beyond the levels of the original DB slider in the left corner of the screen.
Highlight the track like you did in step 3. Now, go to the effect toolbar at the top of the screen and hit effect -> amplify. This will bring up a new menu. Here, you can manually type in how much you want to alter your DB level. Thats it! Happy recording!