Which according to Wikipedia
In 1958 Japan, university professor Tatsuo Kusakabe and his two daughters, Satsuki and Mei, move into an old house to be closer to the hospital where the girls’ mother, Yasuko, is recovering from a long-term illness. Satsuki and Mei find that the house is inhabited by tiny animated dust creatures called susuwatari –- small, dark, dust-like house spirits seen when moving from light to dark places. When the girls become comfortable in their new house and laugh with their father, the soot spirits leave the house to drift away on the wind. It is implied that they are going to find another empty house –- their natural habitat.
This is how it begins, and what you get is a great story of fun and magic. Take what happens when one of the girls disappears. Totoro sends a 8 legged cat bus to save her. That is just 1 of the magical moments in this film, to list all of them, I basically have to tell you the entire film.
Anyway just enjoy the trailer
I also want to make it clear the film has been dubbed into English