Google Cloud Platform is a provider of computing resources for deploying and operating applications on the web. Its specialty is providing a place for individuals and enterprises to build and run software, and it uses the web to connect to the users of that software. Think of tens of thousands of websites operating on a network of "hyperscale" (very big, but also very divisible) data centers, and you'll get the basic idea.
When you run a website, an application, or a service on Google Cloud Platform (GCP), Google keeps track of all of the resources it uses -- specifically, how much processing power, data storage, database queries, and network connectivity it consumes. Rather than lease a server or a DNS address by the month (which is what you would do with an ordinary website provider), you pay for each of these resources on a per-second basis (competitors charge per-minute), with discounts that apply when your services are used heavily by your customers on the web.