An example of a junior is a 15 year old as compared to a 60 year old.
An example of a junior is a person who will be a senior in high school next year.
An example of junior used to describe someone is name of a man named Edward James Finch Jr. whose father is also named Edward James Finch.
An example of junior used as an adjective is in the phrase "junior secretary," which means a secretary who works for a senior secretary.
A junior sports league.
A junior officer; the junior senator.
The junior class.
A sister four years my junior.
A junior partner, a junior lien.
Four years his junior.