Please do your own research on these terms. there are many resource on either topic on the interwebs.
Full-stack just means that you have an understanding of all stages of development. You could take an idea and turn it into a released product with no help.
DevOps is a methodology or set of practices to undertake during development.
The two or not mutually exclusive and are barely even related.
DevOps - Wikipedia
What Is A Full-Stack Developer? | Codeup