To adjust the volume of a clip, to make it louder or mute it, or to create a audio fade in our out, right click on the clip and in the Volume menu and select the appropriate option.
To edit audio separate from video, right click on a video track and in the Separate Audio menu, select either Single Clip or Multiple Clips. Single Clip will place all the audio channels in a single clip. Multiple Clips will create a clip for each audio channel - usually 2 clips for the right and left channel.
You can then edit and position the audio clips like you can with video clips.
You can add music from an MP3 or other music file to your project. First, add the music clip the same way you would a video clip. Then, drag the audio clip from the Project Files panel to the Timeline. You can then edit the clip and position it the same way you would a video clip.
Remember: if you are producing this for publication on a platform such as YouTube or Facebook and use copyrights music, there is a high chance that your video may be removed or you will have your video's audio stripped. You can avoid this by using Public Domain or Copy-Left music. Checkout our Copyright and Fair Use Guide for help finding music.