The areola is the darker area surrounding the nipple.
The size and colour of the areola differs greatly from girl to girl. It can be small as a euro or big as a beer mat, while the colour varies from light pink to brown and black.
In the breasts are no muscles, except for the one around the areola. When you are cold or excited it contacts, decreasing the size of the areola and making your nipple stands out. This also happens with breastfeeding, making it easier for the baby to hold on to the nipple.
Around the areola there are hair follicles. So most girls have some hairs around the nipples. If you don’t like them you can pull them out. This is easily done with a pair of tweezers.
The little bumps around your areola are the glands. They can increase a little bit in size during the second half of your menstrual cycle, making them somewhat more visible.