# How it works
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Amazon Comprehend uses a pre-trained model to gather **insights** about a document or a set of documents. This model is continuously trained on a large body of text so that there is no need for you to provide training data. 

You can use Amazon Comprehend to build your own **custom models** for custom classification and custom entity recognition. You can use [Flywheels](flywheels.md) to help manage the custom models. 

Amazon Comprehend provides **topic modeling** using a built-in model. Topic modeling examines a corpus of documents and organizes the documents based on similar keywords within them.

Amazon Comprehend provides synchronous and asynchronous **document processing modes**. Use synchronous mode for processing one document or a batch of up to 25 documents. Use an asynchronous job to process a large number of documents.

Amazon Comprehend works with AWS Key Management Service (AWS KMS) to provide enhanced encryption for your data. For more information, see [KMS encryption in Amazon Comprehend](kms-in-comprehend.md).



**Topics**
+ [Insights](concepts-insights.md)
+ [Amazon Comprehend Custom](concepts-custom.md)
+ [Topic modeling](topic-modeling.md)
+ [Document processing modes](concepts-processing-modes.md)