To some they appear to be like the folders on your computer but unlike those folders each bucket name must be 100% unique across all of Amazon S3. There are other restrictions as well. Bucket names can only contain lower case letters, numbers, periods or dashes and they are limited to no more than 255 characters in length.
Because of the need for uniqueness in the bucket name it is highly unlikely that I would be be able to create a bucket named “steve” as that name is probably already taken.
However, If I used the filezoomer.com domain name as a part of my bucket name I can (and have) created a “steve.filezoomer.com” bucket. Using a domain name, or some other unique identifier makes it much more likely that your bucket name choices will be available to you.
You can have up to 100 different buckets in a single S3 account and each bucket can hold its own files and folders.
The bucket name you create will also be a part of any file sharing URL you’d use so creating a bucket name that makes sense to your friends and colleagues will make those URLs easier to understand.