A schedule in simple terms is a list of a project's tasks and milestones along with its intended dates and resources who will perform the tasks. Without a full and complete schedule, a project manager will be unable to communicate the big picture, in terms of cost, resources and time lines, necessary to deliver the project.
Creating and managing project schedules can often be an overwhelming exercise. Once you understand the basics of scheduling, you will be better able to work with your projects.
To allow project managers a good amount of flexibility with their schedules, Celoxis offers the following two ways:
Manual Scheduling: With manual scheduling, the dates entered by the project manager are never touched by Celoxis. They simply never change. This provides the project manager with even more control over the schedule. For more details click here.
Auto Scheduling: With auto scheduling, the project manager understands that there could be a number of external factors that can affect task dates and allows Celoxis to automatically perform scheduling calculations. For more details click here.
All tasks are manually scheduled by default. To switch to auto scheduling, click on the Project's actions 
and uncheck the New tasks will be manually scheduled option under Options section of Advanced tab.
Still confused as to which scheduling mode works best for you? Click here to see more examples.