What is it called when authors add more details to help their readers understand a topic

Which part of the story shows how kiara and tanya's differences affect their friendship? kiara and tanya were the best of friends. when they were 10 years old, they always went everywhere together. all their friends knew that if they found one of them, they would find the other. anyone who didn't know them thought that they were twins because both kiara and tanya had long, silky red hair and pale complexions. they were even similar in height and build. they were more like sisters than friends. but as similar as they were in appearance, they were just as different when it came to their personalities. this difference didn't affect their friendship, at least not for a long time. kiara always got out and participated in activities and competitions. tanya was happiest when reading a book at home. kiara was outgoing and talkative. tanya was quiet and shy. kiara was popular, and people were drawn to her because of her ability to make quick friends. tanya hardly had any friends besides kiara. as they grew older, kiara managed to make a large group of friends. tanya, on the other hand, still remained shy and reserved. this difference in their personalities eventually caused a rift between the two friends. tanya would refuse invitations to parties and movies that kiara invited her to. she just didn't want to hang out with people she didn't know that well. kiara couldn't understand why. she thought tanya disliked her friends. eventually, kiara and tanya both realized that they had outgrown one another. they still remained friends, but they were not as close as they once had been.