What was added to silent movies, other than titles, that had a major impact on the the movie industry? The answer is music. Music has transformed many a run of the mill scene into something with stature and substance. Music can set the tone of the scene, or it can overpower it and snuff the life right out of it. What determines what you end up with is the editor. Video and audio editing controls volume, mix and the choice of music for the particular scene. The editor is the "conductor" of the music as it applies to the scene.
Music is available from a multitude of sources. The internet and CD's come to mind first. You should have no problem finding sources
for the music that you want to use that are copyright free. The problem will be in making the decisions of what to use, rather than finding music to use. Video editing is All you have to do is stay
about choice, subtlety, and effect. The key thing to think about is how the music you choose effects the scene that you are putting it under. The purpose of adding music is to enhance
the scene and to better tell the story.
Once you have chosen the music and cut it in under the scene, you have to "mix' the music to fit the scene. Sections of the scene without dialogue can be played at a higher level than sections with dialogue. Yo want to reach a happy medium between music and dialogue, so that the music does not "fight" the dialogue. It is usually a good idea not to have lyrics under dialogue, because they tend to muddle and "fight the dialogue.
Practice with different pieces of music under the same scene and you will soon recognize what works and what doesn't. Have fun with it and don't be afraid to experiment. Professional video editing tricks and techniques will have you laying in sound tracks that draw out the true emotion of your videos.