Two sidebar switches allow you to display a demo goal line (target line) and/or a goal range (target range or target area) on most chart types. Locate chart templates dedicated to them using the GoalLine and GoalRange search keywords.
Most charts with one single series do not need a legend. The series is already self-described by the chart title and the axes titles. Legends may be certainly useful in multi-series charts, where they help identify what each color represents.