When posting job for project there you have to write job description. It should be short self-explanatory. It should have all information about the project.
It should be unambiguous/ clearly concise info what actually you want.
Briefly explain project requirements while writing a description.
A job description should explain the purpose, nature of project.
What is scope of project?
Deadline of project
Briefly explain what are the features and functionalities you want in a project.
You can define technologies, operating environment.
Any design or color scheme in your mind?
You want to start this project from scratch or modify existing one.