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!
This document from the Department of Communication at the University of Washington is a good example of what you might be expected to include in a proposal.
What Is the Purpose of a Proposal?
The purpose of a proposal is to convince your dissertation or thesis committee that you are ready to start your research project and to create a plan for your dissertation or thesis work. You will submit your proposal to your committee for review and then you will do your proposal defense, during which you present your plan and the committee asks questions about it. The committee wants to know if your research questions have academic merit and whether you have chosen the right methods to answer the questions.