Unable to attach database to Amazon RDS using SQL Server Management Studio 2016
With Amazon RDS, you don't get direct access to the underlying filesystem.

If you have an existing database that you want to migrate into RDS SQL Server, rather than using the MDF/LDF files, you'll need to do a restore instead. 

Amazon's instructions to restore a database are pretty good, but since you're asking this question, I'm guessing I probably need to fill you in on a background concept. Remember how I said you don't get access to the filesystem? Well, you can get access to OTHER file systems, kinda like how mapped drives work in Windows. S3 is Amazon's simple storage service where you can create buckets and put files in 'em. You're going to need to:


Create an S3 bucket
Put your database backup (not MDF/LDF) in the bucket
Give your RDS instance permission to read from that S3 bucket (that's where Amazon's instructions come in)
Use Amazon's custom stored procedure rds_restore_database to restore the backup