It boost the Special Defense of rock types. Also when a Pokemon has a certain ability that works in the sand they get that boost. All sandstorm information can be found Here. Pokémon with the Sand Rush Ability have their Speed doubled, while Pokémon with Sand Force get a power boost of 30% for their Rock-, Ground- and Steel-type moves. Pokémon with the Sand Veil Ability increase their Evasion by 1 stage (25%) and are immune to Sandstorm's damaging effect.
No, that is not true. However, a Pokemon with Sand Force in sand will have Rock, Steel, and Ground moves powered up, and Rock types have their special defense raised by 50%.