Growing up and developing sexual feelings is different for
everyone.
When a girl reaches puberty there are big changes not just
to your body but also to your mood and your emotions. It's
important to know about the changes that are coming. 
There's lots of useful information about the physical changes
for girls during puberty here on the Brook website. There's
good information on breast development, understanding your vulva
and vagina, periods, vaginal secretions, masturbation, hygiene,
getting taller, growing body hair and lots more.
You can also find out more about wet dreams for girls at Teenage
Health Freak.