Add relationships between activities to create a path through your schedule from the first activity (or activities) to the last. If you display relationship lines you can add relationships by drawing the relationship on the Gantt Chart from predecessor to successor. You can also add relationships using the Predecessors, Successors, and Relationships tabs in Activity Details, or using the Assign Toolbar.
Relationship lines
Relationship lines graphically illustrate the links between activities in the bars area. You can display relationships lines in both the Gantt Chart and the Activity Network.