Lag (lag time: A delay between tasks that have a dependency. For example, if you need a two-day delay between the finish of one task and the start of another, you can establish a finish-to-start dependency and specify a two-day lag time [has a positive value].) and lead time (lead time: An overlap between tasks that have a dependency. For example, if a task can start when its predecessor is half-finished, you can specify a finish-to-start dependency with a lead time of 50 percent for its successor [has a negative lag value].) enable you to be specific about the time relationships between your tasks. You can set up gaps between linked tasks, or have them overlap.
In this demo, I insert a 2-day gap between two tasks, and create an overlap between two tasks using a percent value.