The place to go to look for any info relating to the best eeveelution pokemon in the game.
Starting with the basics, Sylveon is one of the Eeveelutions. So to obtain a Sylveon, you need to first obtain an Eevee. While you are at it, make sure to bring some exp candies, ingrediants, and more. This mostly revolved around evolving Eevee to Sylveon in Sword&Shield. Level up or find a way to give your Eevee a fairy-type move. Oh and don't forget that you don't need to get a female Eevee either as either gender can evolve to Sylveon. More on the next sub-section.
So you finally got your Eevee with a fairy-type move, what now? Well you simply battle, travel, or eat curry with your furry friend. Basically, you want to level up your friendship with your Eevee. You literally evolve Eevee into Sylveon with the power of friendship! How cute is that?! If you are impatient, simply battle random pokemon and then go back to camping and feed your Eevee. If you are lucky, the camping experience will even level up your Eevee without the need of exp candies. You also interact with your Eevee as that will provide more friendship points. Keep doing this until you interact with Eevee and see 3 hearts pop up on top of Eevee's head. That is when you know it is ready to level up. Level up your Eevee via curry or exp candies and you will get yourself a Sylveon. YAY! Still need more help? Check out the video below!