How does connecting an interface give us the corresponding behavior?

Through a protocol.

A protocol defines a contract of behavior — requirements for properties, methods, and other aspects of an object. A class, structure, or enumeration that implements a protocol guarantees compliance with these requirements.

// Protocol definition
protocol Serializable {
    // Required property
    var dataRepresentation: Data { get }

    // Required method
    func serialize() -> Data
}

// Protocol implementation in a class
class User: Serializable {
    var dataRepresentation: Data {
        // Logic to get Data
        return Data()
    }

    func serialize() -> Data {
        // Serialization logic
        return Data()
    }
}

// Usage
let user = User()
let serializedData = user.serialize()

When working with a data type that implements a specific protocol, we can be confident that it has the required methods and properties defined by that protocol, thus ensuring the expected behavior. Polymorphism allows working with different types that implement the same protocol in a uniform manner.