Story...
And why does Ranma Saotome changes into a girl!?

For those who just join Anime or Ranma 1/2 and say:
Why does Ranmachanges into a girl? Damned!
Well, here's the answer:

When he was young, he was dragged off by his father, Genma Saotome, on a martial arts expedition to China.
One day, they become the unfortunate victims of magical hot springs (Jusenkyo). There are over a hundred springs at this site and each one is cursed.
When you fall into one of those jusenkyo, you take on the body of the first creature to drown into it, but only when you are splashed with cold water.
To undo the tranformation, you have to get splash with hot water. Of course, Ranma fell into the spring of a girl (where she drown long ago) and his father,
well, he changes into a ....Panda! Of course Ranma and Genma are not the only two victims of these cursed springs...

If Ranma didn't changes into a girl, it wouldn't be funny.
(At least there would be Akane to beat him! *^^*)

I recommend you to read the manga or view the series.
There's everything to entertain yourself: humor, romance and action.