A quinceañera is a celebration of a girl's 15th birthday, a young girl transitioning into womanhood. This celebration tends to be very costly. The tradition is celebrated in many Latin American countries with similar and different customs. I'll be referencing to Mexican customs.
Mass
In Mexican culture, a quinceañera celebration begins with a mass in the Catholic church.
The Dress
You'll see the quincenera herself will be wearing a big ball gown, almost a princess like dress. The gown will be a color of her choice and it will match the decorations in her party venue.
Los Chambelanes (The Chamberlains)
The chambelanes are a group of boys that will accompany her through church and throughout her party, where at a point in the evening they will all perform a choreographed dance.
In many quinceañeras, there are at least two choreographed dances, a waltz, and a surprise dance. Depending on the quinceañera herself, she may choose to have damas which would be other young ladies to accompany her as well.
El Valz (The Waltz)
The waltz is one of the choreographed traditional dances performed by the quinceañera and her court. It is learned many months previous to the party to ensure it is perfect for her special night. Many times, families will hire a dance instructor to teach all the dances that will be performed throughout the night.
El Baile Sorpresa (The Surprise Dance)
This is the dance where the quinceañera chooses to dance whatever she wants. She can have a choreographed Hip-Hop dance, Salsa, Merengue, Bachata, or even Jazz! It's any dance style that interests her.
La Ultima Muñeca (The Last Doll)
The quinceañera is given her last doll as she is thought to be too old to play with dolls after the age of 15. In Mexico, once you are presented with your last doll you will dance a short waltz with your doll. A popular song played during this moment would be La ultima muñeca sung by Los Huracanes Del Norte.
The Father Daughter Dance
This is the moment where the quinceañera has her last waltz with her father as a "little girl". WARNING YOU WILL CRY. It's a very special moment. De Nina A Mujer by Julio Iglesias is a very popular song most choose to dance to.
The food
In Mexican culture, the food served for the celebration is chicken with mole others also like to serve carnitas with rice and beans.
The Cake
The cake is similar to a wedding cake, so you can expect it to be big and decorated. The most popular type of cake would be tres leches which is a cake made up of three types of milk.
Shoes and Crown
At this moment the quinceañera begins her day wearing flats, she will have a moment where her parents will replace her flats with heels in front of everyone to show a symbol of growth in becoming a woman. Along with this, she will be crowned as a symbol of coming of age, it is usually done by her mother.