Level design examples
Lots of technical designs focusing little on graphical details and far more on how the player is gonna be navigating the level.
Important thing here is being creative. You have a series of character skills/features and your job is to make the best use of them.
Try to to be gentle when introducing the player to new features but don't be afraid to take clever approaches. Make the player combine his skills to overcome obstacles in his way and do your best to keep the game interesting throughout the whole way.
Level art examples
Make use of a rough project made by level designer and make it beautiful!
Using existing assets or creating your own if needed, fill the level with shape and detail. It is up to you to make this world feel like it's living its own life. You can even try to tell the story using the background. Giving a backstory to specific places is but a one of many ways you can improve the game.