You can set a baseline with the help Milestone Gantt chart.
- Navigate to a project and then select Reports > Milestone Gantt.
- Click
in the upper right corner.
- Click Set Baseline.
- Enter the baseline name and click Set Baseline.

- A baseline is created with a set of open tasks available in the project.
- Tasks without start or end dates are not included in the baseline.
- A user can set upto five baselines.
- Only project users can create a baseline. (Client users are restricted.)