Visual planning in the Gantt chart
Many attributes of tasks can be edited directly with the mouse in the Gantt chart. When you put your mouse pointer on a task bar, controls appear for manipulating the task.
Changing the chart's scale
You can zoom the Gantt chart (and the resource timeline) in and out using the magnifying glass menu in the upper-right corner of the chart, or by putting the mouse pointer in the chart's header area and dragging left or right, as if you were resizing a column.
Rescheduling tasks by dragging 
Grab the middle of a task bar, any part of it away from the controls.
Drag sideways to move the task in time. You can hold Shift while dragging to snap to round values.
Drop the task at the new date and time.
When you move a task like this, its scheduling method in the Task Information inspector changes to "on specific date" and the task tries to maintain its new manually-set start date.
Changing the duration of a task by dragging 
Grab the little traction pad at the right end of a task bar.
Drag the end of the bar left or right to change the task's duration. You can hold Shift while dragging to snap to round values.
Adjusting task completion by dragging 
Grab the white, house-shaped handle on a task bar.
Drag the handle to update the completion.
Drawing dependency lines between tasks 
Put the mouse pointer over a task bar in the Gantt chart to see the mini dependency lines.
Drag a mini dependency line from the beginning or end of one task.
Drop the line onto the beginning or end of another task to create a dependency.
Drawing constraints on tasks 
Hold Shift and drag from the beginning or end of a task to create a start or end constraint.
Hold Shift and double-click an existing constraint to remove it.
Changing the labels on items in the chart
You can customize the data that appears on the sides and on top of tasks, groups, and milestones in the Gantt chart. Just choose View Options from the View menu and use the pop-up menus on the right side of the VIew Options panel.