Salt is currently merely usable as the brightest white building block in Creativerse with many slightly visible rills on 4 sides, but not as a raw material for crafting.
You can also place single blocks of Sand into a pool of liquid Lava, and the the intense heat produced by the Lava will turn the Sand into Salt. The Sand needs to touch liquid lava on three sides in order to be changed into Salt.
Salt can also be crafted in your Crafting Menu (default key "q") after the according crafting recipe has been unlocked by
- crafting an Obsidian Mining Cell or finding one in an Iron Treasure Chest, or (rarely) obtaining one by pet-harvesting a Silver Keepa or a Golden Keepa
- mining Saltrock from the Stalactite layer underground, which requires at least an Obsidian Mining Cell or better to be equipped
- crafting Limestone Walls
To craft 8 blocks of Salt at a time, you'll need (as of R44 in June 2017)
- 4 (blocks of) Saltrock mined from the Stalactite layer, which requires at least an Obsidian Mining Cell to be equipped or better
- 1 (block of) Limestone mined from the Fossil layer, which requires at least a Stone Mining Cell to be equipped or better
- 1 Glob of Goo made from Mold in a Processor or looted/harvested from many creatures