Does Inbound Data Tranfer means "Upload to AWS" and Outbound means "Download"?

Yes. I wrote a script that does uploads and downloads, but costs are more complicated than just that. They charge for storage if you use S3 to store your data. Downloads they charge for. There are a number of ways they charge us. I would recommend that you set up an account and get familiar with AWS cost explorer https://aws.amazon.com/aws-cost-management/aws-cost-explorer/ and set up budgets that flag you when you exceed a certain amount https://aws.amazon.com/aws-cost-management/aws-budgets/. If you are uploading to an S3 bucket, you'll need to set up lifecycle rules on each bucket to delete failed multipart uploads. Instructions are here: https://aws.amazon.com/blogs/aws-cloud-financial-management/discovering-and-deleting-incomplete-multipart-uploads-to-lower-amazon-s3-costs/