When you add lag time, you delay the start time of the successor task.
When you add lead time to a task, work on that task will overlap work on its predecessor.
Before you can start adding lead or lag time, you need to create a dependency between the two tasks. In most cases, your dependency would point from the end of a task, the predecessor, to the beginning of another task, the successor. This is an end-to-start dependency.
in end-to-start dependencies such as the below, "moving" the predecessor will automatically move the dependent task (successor).
Here’s how lag time looks in the Gantt chart (1 day lag time):
Here’s how lead time looks in the Gantt chart (2 days lead time):