YouTube will generally take care of the licenses required to stream so-called "user-generated content" incorporating music from its website, so we don't need to issue you a license directly. However, if your video is of a commercial nature (i.e. promoting a product, brand, or political view) you WILL NEED to get a license from us. But in cases of user-generated content that incorporates our music, you may see a content claim show up on your video. This means that we allow you to use it but as the owner we can monetize your video (place ads around it).
To find out what music policies are on our music catalog check out this informative video: