Legend can be turned on/off via toggle.

Legend typically displays series in a chart with a predefined marker and the name of the categories/series that are represented in the chart.

With the advanced version of the chart you can customize the legend to suit your needs and style, by changing its:

Currently if you see 3 dots in the legends block, it means that some of your legends did not fit in the block. To see the hidden legends, you have to change the Height or Width property, or resize the chart container