Follow these steps in order to learn how to store a username and password in AWS Secrets Manager:

1. Log in to your AWS account, and go to the AWS Secrets Manager dashboard.
2. Click Store a new secret.

3. Select Other types of secrets:

4. Add your secret key/value pair in the Plaintext box. Go with the default for the encryption key:

5. Click Next.
6. Give the secret a Name, optional Description and Tags, and click Next.
7. On the next screen, Disable automatic rotation, and click Next.
8. On the final screen, review your settings and copy any code snippets that you might need for your application. The following is a simplified version of the JavaScript example:

var AWS = require('aws-sdk'),
    region = "us-east-1",
    secretName = "MySecret",
    secret,
    decodedBinarySecret;

var client = new AWS.SecretsManager({region: region});

client.getSecretValue({SecretId: secretName}, function(err, data) {
    if (err) {
        throw err;
    }
    else {
        if ('SecretString' in data) {
            secret = data.SecretString;
        } else {
            let buff = new Buffer(data.SecretBinary, 'base64');
            decodedBinarySecret = buff.toString('ascii');
        }
    }
    // Your code goes here. 
});

9. Click Store to complete the process.

You now have a secret that is securely stored and encrypted using the Key Management Service (KMS). If you already have a Relation Database Service (RDS) database created in your account, experiment with secrets that are automatically integrated with RDS. This is a huge improvement over storing usernames and passwords in configuration files or environment variables!