Lambda allows real-time event processing from various event sources like S3, DynamoDB streams, and Kinesis streams. Events can either be pushed to Lambda through asynchronous or synchronous invokes, or pulled from streams using Lambda's polling logic. Lambda processes streams efficiently by sub-batching records into invocations and processing shards concurrently with retries. Thomson Reuters used this to build a scalable usage analytics solution on AWS that processes millions of events daily from their products, automatically scales, and requires little maintenance.