How do girls' breasts develop during puberty?

Women's breasts come in many different shapes and sizes. When entering puberty in girls, from a "flat" chest, girls' breasts will gradually grow larger and become "double mountains". So how do girls' breasts develop during puberty and what should be noted?

Physical Development during Adolescence

How Girls Are Developing Earlier In An Age Of 'New Puberty' : Shots - Health News : NPR

Text - Puberty: Normal Growth and Development in Girls

How do girls' breasts develop during puberty?

I only grew one boob during puberty and doctors can't tell me

How to Know when You Are Going to Start Puberty (Girls)

How do girls' breasts develop during puberty?

Understanding Breast Development During Puberty

Children's book says girls grow breasts to make them attractive to