editing sound to movie

i opened a file from public file called jung fu fighting and added sound into garage band then placed the movie into garage band then cropped some of the sound down to 30 seconds by selecting some of the sound and pressing back space or edit delete, i made the sound at the end of the movie fade by going to track then fade out. next i saved the file into my documents and exported the movie so i could watch it on quicktime player and so i can upload it to my blogger for others to view.