Amazon DocumentDB is a fully managed, scalable, and highly available document database service that is designed to be compatible with the MongoDB API. It is a NoSQL database that is optimized for storing, indexing, and querying JSON data.
DocumentDB is designed to be highly available and scalable, with the ability to handle millions of requests per second. It also provides features such as automatic failover, point-in-time recovery, and continuous backup to improve reliability. 

To get started with Amazon DocumentDB, you will need an AWS account. If you don't already have one, you can sign up for a free trial at https://aws.amazon.com/. 

1. Once you have an AWS account, you can create a DocumentDB cluster in the AWS Management Console by following these steps: 
2. Go to the Amazon DocumentDB page in the AWS Management Console (https://console.aws.amazon.com/docdb/). 
3. Click the "Create cluster" button. 
4. On the "Create cluster" page, enter a name for your cluster and select the MongoDB version you want to use. 
5. Select the instance class and number of instances you want to use for your cluster. 
6. Select the availability zone where you want to create your cluster. 7. Choose a database authentication method and enter a password for the admin user. 
8. Choose a security group and VPC for your cluster. 
9. Review your cluster settings and click the "Create cluster" button. 

It may take a few minutes for your cluster to be created. Once it is ready, you can connect to it using the MongoDB API or a MongoDB client library and start working with your data. To connect to your DocumentDB cluster, you will need the connection string and credentials for the admin user you created. You can find these in the AWS Management Console on the "Clusters" page. 

You can also use the AWS CLI or SDKs to create and manage DocumentDB clusters. The AWS documentation provides more detailed instructions and examples of how to do this.