During adolescence, body is changing from a girl to lady capable of fertility.these changes are happening at fast pace and if you are not aware you will feel shy,insecure,scared and confused.
This time is called puberty. For girls usual age is from 11-16 years .Sometimes it can start as early as 7 yrs too.it takes many years to complete the process .First sign of puberty is growing breast,then growing body hair in private parts and axilla, growth spurt, changing body shape and getting periods.