Lesson 8 of Practical Compositing in Nuke demonstrates the rotoscoping toolset.
For the complete lesson, go to https://learn.foundry.com/course/4689/view/roto
For the full course, go to https://learn.foundry.com/nuke#practical-compositing-with-austin-meyers
For Nuke product information, go to: https://www.foundry.com/products/nuke