S3 is object-based flat file unlimited storage. It's unlimited, but that doesn't mean we should throw files up there without thinking -- storage still costs money. It's not block-based, so it's not meant for storing operating systems or live databases. But any type of file can be stored (including database file backups), and each can be from 0 bytes up to 5 TB. General knowledge about S3 is one of the key categories in the AWS Certified Cloud Practitioner exam.
In my last article, we discussed the support options' costs and EC2 pricing. This is a large topic, so I'm going to have to have a 3rd part since S3 takes up a lot.
I don't believe the exams will ask about specific prices, as these can always change. But the important thing is understanding the relative pricing, so you could be able to make intelligent cost analysis decisions.