I don't know exact details on how it works but here is a shortened version:
A few ZTA representatives will come to your school. They will interview interested women and have meet-and-greets with them. From there, they will narrow down the pledge class.
ZTA is one of the largest (in number of chapters and initiates) panhellenic sororities. We were founded in 1898.
If you have anymore questions, don't hestitate to ask!