How do I install the AWS SDK for Node.js and the DynamoDB DocumentClient?

First, ensure you have Node.js and npm installed. Then, run `npm install aws-sdk` in your project directory. The DynamoDB DocumentClient is part of the AWS SDK, so no separate installation is needed. You can then require the AWS SDK and create a DocumentClient instance: `const AWS = require('aws-sdk'); const documentClient = new AWS.DynamoDB.DocumentClient();`