DigitalOcean have pretty good articles/docs on both Snapshots and backups. You can check them by using the following links:
Now, the basic differences are
Backups are taken once per week, and each backup is retained for four weeks. tBackups are stored in the same datacenter as the corresponding Droplet.
You can enable backups for any Droplet, but they may not be ideal for Droplets with heavy I/O workloads, such as database servers, because disk writes have degraded performance while the backup is being created.
Snapshots provide a full copy of a DigitalOcean Droplet or volume. Creating a snapshot saves everything from the Droplet or volume’s disk to a disk image saved in your DigitalOcean account. They’re an easy way to archive a Droplet or volume at a point in time.
You can use snapshots to create new Droplets or volumes with the same contents of the snapshot. You can back up the contents of a block storage volume, restore a Droplet to the point in time when a snapshot was taken, or migrate a Droplet to a different region.
For more information, I’ll recommend going through the docs. If you still have some questions after reading them, please ask as much as you want!