I am new to after effects but have figured out most of the features through trial and error but I am trying to learn how to do different effects. One that I am trying figure out is to add a friend of mine to a scene in a movie by using a video shot of him without a green screen. In other words, I'm trying to do something along the lines of taking a video of my friend running down the street and add him to a scene from Captain America Civil War where he runs into battle.
If you need to extract a moving object (or a person) from a video that was not shot on green screen, you need to use 'rotoscoping'. This means manually cutting out your friend from the footage frame by frame. You can use tools such as MochaAE (included in After Effects) to make this a little easier. Here is a tutorial on how to use it: