The addition of music to your film or video can add a lot! Unfortunately not all of us have the knowhow or the tools to make our own music. That where royalty free music comes in. Royalty free music can often be expensive, but there are a few sites that let you download this music for free!
My personal favorite is incompetech.com. With this website you can browse through music by genre or even moods for your movie. All that is required is that you credit the composer and the website. A lot of the music may even sound familiar to you as this is a popular website for youtubers to use. I used music from this site for Once Daily and The Dragoon Films Trailer.
Here are a couple other free music sites that I discovered that only require that you credit the website to use:
There are a lot of options out there! Now go on and score your movie!