Although the wording of your question is a bit cryptic (in that I am not sure if you want quotations of their introduction during the exposition of the plot or the true "how" they are introduced in regards to characterization), I am going to assume you mean the true "how" of how they are introduced in regards to the important aspects of their character. Maleeka, Ms. Saunders, and Charlese are vivid characters from the very start.
Malleeka, as the main character, is originally introduced to the reader as a darker-skinned African American girl in middle school who has very low self-esteem as a result. We know, as readers, that her self-esteem is low because of the interjected comments she makes as part of her thought process.
[I feel like] someone stuck a note on my forehead saying, losers wanted here ... folks can't help but tease. ... [I am] the darkest, worse-dressed thing in school. I’m also the tallest, skinniest thing you ever seen.
Charlese, otherwise known as "Char," is introduced to the reader as an immediate bully. It might seem an irony that Maleeka beckons friendship with her, but Maleeka needs protection, so her attraction to Char as a friend really shouldn't strike the reader as strange at all. However, because Char is a bully, this is not a good friendship choice for Maleeka.
Miss Saunders is originally introduced (and continues to remain) a support for Maleeka. Miss Saunders has empathy for Maleeka (not just sympathy for her) because Miss Saunders is sometimes teased as well. Miss Saunders is always in support of Maleeka even if Maleeka herself resists the idea that she can be beautiful and intelligent and graceful.
In conclusion, we can say that Maleeka is introduced as a pre-teen with low self-esteem, Char is introduced as a bully, and Saunders is introduced as a support. Together they create an interesting threesome that makes the book worth the read.