2 Questions:
how do you overlap sound?
Answer: drag the second part of the sound to the first and then it will touch. then let go of it and grab it again and then drag the second one over the first sound click.

How do you take one frame of the video clip and use it as a picture?
answer: go to the right hand corner and then you will see a button with a camera on it. click it and then you have a still picture.