HDDs and SSDs have major differences in terms of:
Technology: HDDs use magnetic disks to store data persistently whereas SSDs use integrated circuit assemblies. In contrast with HDDs, SSDs have a limit on the amount of data that can be read and written on the drive.
Price and Capacity: Currently SSDs are much more expensive than HDDs. For this reason, high capacities are most commonly found on HDDs, since they are much more affordable than SSDs.
Speed: SSDs are a lot faster than HDDs.
Durability: Although there isn't any clear evidence on which type of drive experiences the most hardware failures, SSDs are much more resistant to shock and sudden drops than HHDs, since they don't contain any mechanical parts.