Creating a predecessor/successor link can be done in several ways. The first and easiest is to use the mouse to link tasks . The first task here applies a link in the Gantt Chart view. The second task shows you how the same method for creating a link with the mouse applies in the Network Diagram view (except that no ToolTip will appear).
Create a Link in Gantt Chart View
Center the mouse pointer over the middle of the Gantt bar of the task you want to become the predecessor, and then hold down the left mouse button.
Now drag the pointer to the middle of the Gantt bar of the task you want to become the successor.
Notice that the ToolTip that appears tells you which two tasks you are linking.
Release the left mouse button and the two tasks are linked.