There are a number of tutoprials that you can check out here with information on greenscreening.
I have made a few myself, and have posted the links below. CLab tutorial Grenscreen Basics Lighting a Green Screen
^^I know a few of mine are done on bluescreens, but the idea is pretty much the same. And green screen instructions are included.
Hope those help! Thought here is a bit of a learning curve with CLab, you'll get it. Don't freak if it takes a little while, it will take practice.
Sorry, I don't quite understand what you are asking. Are you wondering how to import videos into CLab to then composite? If so, you need to use your NLE or video editor to capture them video from your camcorder and then you can cut it and edit it to the length you need. Export/render the video as .avi or .mov. Then you open the Composite Lab program, and you choose your video file that you rendered. Add your greenscreen effect, grading, ect then render it again. Open yout NLE and import the edited clip. Now you can add more scenes and cut more.