The project brief is to ensure that your entire team is on the same page with respect to project details. Though it is non-mandatory, it is a great idea to fill it as much as possible. So get articulate and detailed when you start filling up your project brief.

Step 1 - Go Roadmap > plan > Brief activity

or Step 1 - Go to project > Project Brief

Step 2 - Add Description, define your problem statement, project background, and challenges 

Step 3 - Associate vision. This is where you can link your larger business visions to your project. You can pick from the existing or create a new one.

Step 4 - Add project scope. Identify your major deliverables, add your milestones and monitor these throughout the project.

Step 5 - Add target users and audience

Step 6 - Change designs process if needed. This can be done only if the project is in not started state

Step 7 - Add custom sections, sponsors, competitors etc