Simple:
* The citizen was proud to vote in the upcoming election.
* Every citizen has the right to free speech.
* The city council held a meeting to address concerns from its citizens.
More complex:
* As a responsible citizen, I believe it's important to recycle and conserve resources.
* The activist fought for the rights of all citizens, regardless of their background.
* The new law was designed to protect the safety of all citizens.
* The jury was composed of twelve citizens who had been carefully selected.
Figurative:
* The trees are citizens of the forest, each playing a vital role in the ecosystem.
You can also use "citizen" to describe someone who lives in a particular country or city, even if they don't have full citizenship rights.
For example:
* The citizen of Paris enjoyed the sights and sounds of the city.
* The citizen of India was visiting the United States for the first time.