As stated earlier users need to have access to at least one project before they can log into the i2b2 Web Client or Workbench. The Project User page simply captures the name of the user that has access to the project.
Before you can add a user to a project they have to be entered into the i2b2 Admin as a user. Please see the section titled Manage Users for information on adding a user to the i2b2 Admin.
Once you have added a user to the project you will need to define their role within it. The i2b2 roles determine the level of access a user has within a project.
In addition to roles, you can also add Project User Parameters. Although these parameters are entered on the "user" they are specific to the user and the project. Whereas User Parameters are specific only to the user.