In order to use RML Amazon S3 Pro extension, you need to create at least one S3 bucket. Here are the steps to create S3 buckets.

1. Login to your AWS account online as you would normally do

2. Access your S3 Management Console

3. Click on Create bucket button.  Then insert a bucket name and select a bucket region from the drop down list. Click Next.

S3BucketCreate

4. The Set properties screen is up to you.  You can keep every options disabled and enable them if needed later. Click Next when you are done.

5. Now the permissions screen is also up to you. However, you probably want everyone to be able to read objects in the bucket if you want your website to be able to display them properly.

S3BucketPerms

6. Confirm your bucket name, region, properties and permissions and then click Create bucket button. Make sure you grab your bucket name and region. 

S3BucketReview

7. You bucket name and region along with your Access key ID and secret shall be entered when you create a new Amazon S3 Pro Remote Media Library in WordPress (Media > Remote Libraries). See this tutorial to learn how to create an Amazon S3 Access key ID and secret

8. Finally, verify that your bucket CORS configuration allows uploads from your domain. Learn how to set buckets CORS configuration in this tutorial.