As a noun:
* The musical duo performed a beautiful rendition of "Hallelujah."
* The comedy duo had the audience in stitches with their witty banter.
* The duo of detectives worked tirelessly to solve the case.
* We saw a duo of eagles soaring high above the mountains.
As an adjective:
* The restaurant offers a duo plate, featuring two different entrees.
* The duo championship was fiercely contested between the top two teams.
* We're planning a duo trip to Paris, just the two of us.
Note: "Duo" is typically used for two individuals working together, but it can also be used for pairs of things, such as musical instruments or objects.