S3 (Simple Storage Service) keeps files for you. You hand it some bytes and a name; it stores them across several zones and hands them back whenever you ask. The Monster Market's website will live in S3.
Buckets and objects
A file in S3 is called an object. Objects live in a bucket: a container with a name, in one region.
A bucket's name is unique across every account in the world. Names use lowercase letters, digits and hyphens, from 3 to 63 characters. monster-test is surely taken; monster-test-b22a7h is yours.
Making one
aws s3 mb s3://monster-test-b22a7haws s3 is the part of the CLI for moving files. mb means make bucket. The CLI writes a bucket as s3:// and its name. It lands in your default region, us-east-1.
aws s3 lsls without a bucket lists your buckets, with the time each one was made.
If the name is taken by another account, you get BucketAlreadyExists, and you need another name. If you already own it, the code is BucketAlreadyOwnedByYou.
An empty bucket costs nothing. The objects in it cost a little per gigabyte per month.