The proposal, sometimes called the prospectus, is composed mainly of the Introduction, Research Questions, Literature Review, Research Significance and Methodology. It may also include a dissertation/thesis outline and a timeline for your proposed research. You will be able to reuse the proposal when you actually write the entire dissertation or thesis.
In the graduate student timeline, the proposal comes after successfully passing qualifying or comprehensive exams and before starting the research for a dissertation or thesis.
Each UNT department has slightly different proposal requirements, so be sure to check with your advisor or the department's graduate advisor before you start!