With Cloud Functions, you can create your own server-side code in the cloud and execute it whenever you need. The main purpose of Cloud Functions is to complement your client app with business or server-side logic without the need for configuring and maintaining your own servers.
A Cloud Function is very similar to a function in development terms—it can accept parameters and can return values. Each Cloud Function is assigned a unique HTTP URL (endpoint). Using this URL you can call the function, supply arguments, and get a response.
Cloud Functions are great for integrating with external systems, generating reports, and many other scenarios.