Firebase is a mobile and web development platform where you can use it to make your Apps to have a better performance.
It was acquired by Google in 2014.
You can do tasks like User-Authentication, Storage, Realtime Database, Hosting, Analytics, Predictions, Cloud Messaging, Testing and many more using its console.
You can start using Firebase only after linking your app/website with it by placing the necessary code.
Realtime Database:
Its a cloud hosted Database. Data is stored in the form of JSON and is synchronized in Real-time.
Cloud-Storage:
Used to store Server-generated Data including photos, videos etc and you can access the same.
Hosting:
Its a platform to host your web-content(Dynamic or Static).
Authentication:
Used to verify your app-users using any of the method like email-password , Using Gmail, Facebook id, Phone Number etc.
Analytics:
Linking Firebase with Google Analytics will help you to analyse more and improve your app’s performance.
ML Kit:
Brings Machine Learning for Mobile Apps and Websites.
checkout this link for more details.