I have a video of a Screen Capture on my phone, and I have a video of me talking. I want the video of my phone to be next to my face. I have it positioned, but I can't get rid of a black screen. Help!

Simple, use a composite transition between the two tracks with the phone video on top. Watch this youtube video https://www.youtube.com/watch?t=160&v=f6VHlOZutm8

The transition will allow you also to change the position and size of the top video.

Alternatively, there is also the Affine transition. In addition to the Composite transition it allows rotating the top clip before blending it into the bottom clip.