Device is a noun and devise is a verb—both relate to the concept of invention.
A device is a machine—something artificially created, with multiple parts, that does something. It can refer to many things, from smartphones to spaceships—though most often we use the word device for smaller things.
Device can also be used to describe some abstract things that are invented, especially in art and literature. For example, flashbacks, montages, and voice-overs are cinematic devices— devices used in film-making. There are also dramatic devices, literary devices, and poetic devices.
Finally, device can also mean “a trick used to manipulate a person”:
The device of flattery does not work well on me.
To devise is a verb meaning to create or to invent. It can be used about devices, or more abstract things:
It must have been difficult to devise the first wheel.
I have devised an argument that should convince him.