Everything you need.
Rails is a full-stack framework. It ships with all the tools needed to build amazing web apps on both the front and back end.
Rendering HTML templates, updating databases, sending and receiving emails, maintaining live pages via WebSockets, enqueuing jobs for asynchronous work, storing uploads in the cloud, providing solid security protections for common attacks. Rails does it all and so much more.
Active Records make modeling easy.
Databases come to life with business logic encapsulated in rich objects. Modeling associations between tables, providing callbacks when saved, encrypting sensitive data seamlessly, and expressing SQL queries beautifully.
Action Controllers handle all requests.
Controllers expose the domain model to the web, process incoming parameters, set caching headers, and render templates, responding with either HTML or JSON.
Action Views mix Ruby and HTML.
Templates can use the full versatility of Ruby, excessive code is extracted into helpers, and the domain model is used directly and interwoven with the HTML.
Action Dispatch route URLs.
Configure how URLs connect to the controllers using the routing domain language. Routes expose the bundle of actions that go together as a resource: index, show, new, create, edit, update, destroy.
Optimized for happiness.
Rails has united and cultivated a strong tribe around a wide set of heretical thoughts about the nature of programming and programmers. Understanding these thoughts will help you understand the design of the framework.