I want my main character to be Eevee but I do not how to answer the questions so I become Eevee.
That should explain all.
What Pokemon you become is based off of how you answer the question when you begin the game.
Here's a link that'll guide you on how to get a specific item.
Eevee can only be a female and Jolly nature, so when they ask you if youre a boy or a girl, choose girl