Imagine you have 1000 PC/Laptop/Servers in an office containing 1000s of pictures, videos etc, that you need to access on a daily basis (like Google Photos for example). Imagine hosting 1000 such hardware infrastructure. Not only will it be expensive, but also difficult to manage. And to access it you have to go to this office everyday --- not so feasible.
Now imaging you have 1 box (hypervisor) that can host 1000 such virtual servers (such as VMs) hosted on the internet, that you can access from your home/mobile phone anywhere anytime. That is cloud computing. Everything is in the cloud.
As for where to get started, I see others have provided great links. Here's another one: Even if you don't want to take the exam, the resources provided here are good https://www.cisco.com/c/en/us/training-events/training-certifications/certifications/associate/ccna-cloud.html.
Goodluck to you.