A custom is something your family does by habit. One customs is when you put candles on your birthday cake. Also when you get to choose where you want to go to eat on your birthday. Another custom of is when you get to choose the type of birthday cake you get.
On her quincinera, a girl celebrates her 15th birthday. Her growth into womanhood. Her father or fatherfigure removes her young girls shoe and replaces it with a grown-up heel or fancy slipper. This custom represents her fathers acknowlegement of his daughter having ascended into womanhood.