Dear Beth,
Thank you for your letter
My name is (свое имя напиши)
I am (напиши сюда свой возраст) 
I like to play computer games and listen to music
I also like animals and
I have a cat (или любого другого своего животного, если оно у тебя есть), its name is (его имя сюда напиши). It is white. My cat likes to play with its ball. It`s funny and cute.
Last summer I was in Moskow. I had a good time there. I helped my grandma with her chores around the house. 
I`d like to have a computer game SIMS 4 as a present for New Year.
Best wishes,
(твое имя)