Eevee had three initial evolutions when it debuted in Pokémon Red and Blue.
Those first three evolutions were Vaporeon, Jolteon, and Flareon. Each requires a different Evolution Stone: a Water Stone for Vaporeon, a Thunder Stone for Jolteon, and a Fire Stone for Flareon. This branching evolution made Eevee unusual among the original Pokémon species.
Eevee later gained more evolutionary forms. Espeon and Umbreon arrived in Pokémon Gold and Silver, Leafeon and Glaceon in Pokémon Diamond and Pearl, and Sylveon in Pokémon X and Y. The total number of commonly recognized Eeveelutions therefore grew to eight.
The phrase “Eevee’s evolutions” can refer either to the original three or the later total, so the generation in the question matters. Eevee itself is a Normal-type Pokémon, while each of its initial forms represents a different elemental type: Water, Electric, or Fire.