Skills for Shadow of War is covered on this page.
Skills and Abilities available to you have been significantly expanded. Instead of just purchasing a skill and being done with it, you can now modify unlocked skills further via its own upgrades. For example the stealth based Brutalize skill can be upgraded to add an effect that causes nearby enemies to flee in terror once you've landed that savage blow. These upgrades will allow you to upgrade your Talion and Celebrimbor duality to its fullest extant and give your a multitude of new ways to dominate the battlefield.