No offense, but the gaps in your AE knowledge are as big as the Yangtsekiang is long. The Rotobrush creates transparency, the black is just the comp background, but of course you can enable the transparency checkerboard at any time. That being so, you simply put whatever background you want as another layer beneath the RB'ed layer. This is really basic stuff and rather than relying on poorly done YT videos that may skip these basics, perhaps you can find it in your heart to actually read the help files or at least watch some good tutorials on Lynda.com or even older "Basics" series on CreativeCOW, Video CoPilot and some other places?
Previously, I learned to use the Rotobrush and I thought that was the answer to my problem, but it just extracts me and leaves a black background, and I don't want that.
That is wrong, as Mylenium said, you just did not have transparency grid turned on in your Composition Panel so you could not see the transparency. You are also stating that the rooted layer is the background. This is incorrect. The rooted layer is the foreground. You simply put a background layer below it just as you would in any app that uses layers like Photoshop or Illustrator or . . .
If you want to export a movie that maintains a transparent background then you simply choose the Lossless With Alpha preset inside the Output Module and accept the default settings or you take the time to learn about Rendering, Alpha Channels and codecs by typing "rendering" or "Rendering transparent" in the Search Help field at the top right corner of AE and you study up. None of this stuff is hard, but the knowledge will not automatically pour into your head and the options are too many to achieve success by just poking around.
One more thing. There is no media player (Quick Time, Windows Media Player, etc.) that will show you a transparent background in your video. NONE. The only time transparency shows up is in an app designed to use alpha channels like After Effects or Premiere Pro.
Study up here: Adobe - Search: rendering%20transparent
No offense taken. I absolutely agree with you. That is why I asked for help. And I have watched Lynda.com videos and Creative Cow and they were very helpful, but because of my extreme lack of knowledge, did not solve my problem. I barely know Premiere CS6, much less AE, which I just started tackling. Editing is not my strongest talent, but I love it, and the sky is the limit. I just get so frustrated because I know you can't learn it overnight, but I will learn it.
Thank you. I definitely will "study up," because from what you say, I don't know diddly! I know nothing about "lossless, transparency, Alpha Channel," etc. It's all Greek to me. Nevertheless, I am sooo fascinated about what can be done with Premiere, After Effects, etc., I am determined to learn; slowly but surely. Whether you know it or not, it is not easy for everyone to catch onto something so perplex. Yes, for me it is almost as difficult as cinematography itself.
I openly admit my shortcomings, but I do know that I am an excellent, writer/director/producer, and I don't have to be an expert at all these other things, but I do admire those of you who are.