Rotoscoping is the process of tracing over live action video to create an animation. Some animators consider this a lazy way of cheating — and if you are literally just tracing video, that's pretty true. At the same time, this method can be really helpful for animating complicated "3d camera movements" or other challenging actions.
Rotoscoping is most effective when used as just one aspect of an animation. This might be where the rotoscope is used like an underpainting/skeletal structure - or when creating a seamless transition between live action and animation. So when rotoscoping, trace just the information you need and add to it to make something new.