Tough question. Its like asking for a practical example of using a computer. There are so many real-world examples of using Kubernetes(K8S) that describing one sheds little light to a layman on its purpose. Let’s try this.
When computers first came out using microprocessors, programs would be a single thread of execution that the processor (computer central processing unit) jumped into when it powered up. As processors became more powerful with more memory and we wanted to do more with it, programs would run in multiple threads of execution.
But those threads kept getting in each others way so we created operating systems that could track multiple processes, where each processor owned its own resources so one program couldn’t stomp on another program.
Skipping lots of intervening steps along the way, we got to a point where just installing a program became difficult because there was so many potentially conflicting environment issues (shared libraries, versions of tools, drivers etc…), and the network environment became complex making it difficult to manage network connections and security between the programs , and these powerful programs could run amuck starving out other programs etc…
So, we created containers, where a very simple environment exists to install the program. And the containers owned resources making it difficult for one containerized program to impact another container. And we created lots of these containers to solve complex problems. And, just like earlier where we needed something to manage all those programs (the operating system), we needed something to manage all these containers. And that is what K8S does. Its like an operating system for containers (gross simplification).
So, what can you do with Kubernetes. People use it for simple problems, like installing a document conversion systems that scales by deploying more containers (small standalone conversion program instances) when needed to convert more documents. Engineers might deploy build containers in kubernetes to compile and build programs and package containers. People also build up complex deployments of cooperating containerized programs that might implement a system to manage insurance company product offerings to their clients, just to name a few.
You can pretty much do anything in a kubernetes set of containers that you could do in any computer environment, if you want to bear the expense of the compute resources used by kubernetes itself and take on the burden of bringing up and properly managing your kubernetes cluster.