Your question is quite vague/generic.
People store their source code (or generally, files) in git; let Jenkins run jobs (like CI/CD pipelines), use Docker to put their software into well-defined containers, Nagios to monitor their systems, ELK to collect, store and visualize (mostly logging, event) data, AWS to host their stuff, and Chef to manage their configurations.
If you are studying that and learning about it, then you should have gotten that kind of information, really. The scenario in real world companies is simply to use those tools for what they are made, in different combinations as needed.
If you really have just gotten some deficient information from your college or wherever you studied those things, then get a book like The DevOps Handbook and give it a read. It should clear up how all of this would work together in the real world.