Navigate Here: Projects > Browse Projects; select a project > Implementation tab > Schedules tab; Enter into Schedule Gantt Chart, click Save as Schedule Baseline icon 
on the tool bar
A popup screen "Save as Schedule Baseline" will be displayed.
To add a new schedule baseline, first provide the general information by filling in the following fields:
The required fields are noted with an asterisk (*).
Baseline Name*: The name of the schedule baseline. It must be unique under the same project.
Description: The detail description of the schedule baseline.
Once you've finished adding, click the Save button to save the new schedule baseline and the popup screen will be closed.
Click the Cancel button to close the popup screen without saving the new schedule baseline.
Note: Baseline is exactly the same as the current schedule. When a baseline is saved, the entire task list in its current structure, as well as the General, Resources and Predecessors of each task will be copied under the baseline. But task's Documents, Risks, Issues, Timesheets and any cross schedule predecessor relationships will not be saved in the baseline.