To link your Amazon S3 bucket to Platform you need your Secret Key, your Access Key, and the name of your bucket. To get these Keys you will need to create an IAM user within AWS.
Creating an IAM user
First log into your AWS account and select your account name in the top right corner. Then select "My Security Credentials" from the drop-down list.
Then select Users from the list to the left and then click the Add user button.
Enter a User name and select Programmatic access, then click Next.
Select Attach existing policies directly, filter for S3 and select AmazonS3FullAccess, click Next.
Click Next on the Tags screen, on review your User should look similar to the account below, click Create user.
Copy the Access key ID, select the "show" link under Secret access key and copy the Secret Key.
You now have the Keys you need to Link your S3 bucket to Platform