What is the use of the button `PUBLISH` in project planning?

Here is the scenario i am trying.

1. Created a project

2. Created a task without assigning a user

3. Created project planning

4. Assigned a role, time estimate and assign the employee

5. And hit on the PUBLISH button.

I thought the task will be assigned to the employee. But unfortunately, it didn't happen.

Is it possible to assign a task from the project planning?

And what is happening when i hit on the `PUBLISH` button?