EBS is for mounting directly onto EC2 server instances. S3 is Object Oriented Storage that is not constantly needing to be accessed (and is hence cheaper). There is then even cheaper AWS Glacier which is for long-term storage where you don’t really expect to need to access it, but wouldn’t want to lose it.
There are then two main types of EBS - HDD (Hard Disk Drives, i.e. magnetic spinning disks), which are fairly slow to access, and SSD, which are solid state drives which are super fast to access, but more expensive.