Explain Like I'm Five

For many things you need a computer, that runs all the time, that is connected to the internet, that has not too much and not too little performance. You want to run a website, a forum, a file server, a ...? You need just such a computer. Cloud is a large word, that essentially refers to services, where you can easily rent a computer of your choosing for money, to run any and all services on. What you are refering to is probably cloud storage, where the service is, you can send and receive files from a server. The technical details can become complicated, how to ensure the files are always up to date, what if you make different changes on different devices at the same time, do we create a local copy or do we stream all file interactions. But the summary is this: There is a computer somewhere else, running a service, being rented from a cloud provider.