Here are some examples of words with the root "co-":
* Cooperation: working together towards a common goal.
* Coexist: existing together peacefully.
* Coauthor: writing something with another person.
* Co-worker: someone who works with you.
* Co-founder: one of the people who started an organization or company.
Remember that "co-" is often used in combination with other words to create new words with related meanings.