For the S3 target to work correctly, you need to create an IAM user with permission to access the bucket you wish hotglue to output data to. The instructions to create an IAM user are available on the AWS docs.
To begin, head to the flow that you would like to add an S3 source to.
At this point, you should go an enable S3 in the Sources tab of this flow. Do that by clicking the Connect button for the S3 source.
This is the part where you need your credentials from S3.
Plug in the corresponding credentials and hit the Save & Continue button.
You have now set up the S3 source!