One facet of movies or shows that can be super important is the use of green screens, or other screens to fulfill the same variety. These can be used to add in background animations or scenery shots to add some variety into whatever is being edited. First, to add the chroma key, select the clip that you want to add the chroma into. In the effects panel in the bottom right, click on the folder that says "video effects", and then in that folder click on "keying". There are a few different options, but the most simple option would be to select "Ultra Key". Drag this onto the clip in your sequence, and you will now be able to edit the chroma in the clip panel in the upper left corner. Make sure that the background chroma is on the lower level than the clip you want to add it to, so have the clip with the green screen on track 2 and the thing you want to chroma in on track 1. Then, take the eye dropper tool and click on the green, or whatever color you want to chroma out, and at this point, you should see the background change. It still may not look perfect yet, though, as shadows and different lighting conditions might not create a clean chroma. Took fix this, in the same panel as the eye dropper, there should be a few options, like "matte cleanup" with different sliders altering shadows and choke. Once fiddling around with these, your overall shot should be done and looking nice. A good chroma can end up improving shots and adding much needed variety.