Line Charts
A line chart connects a series of data points with a continuous line on a graph. To add a Line Chart Panel, add a Panel (see: Adding a Panel to Dashboard).
Step 1: Select Line Chart Panel

Step 2: You should see options to customise the Title of the chart, data source for the Panel and parameter to Group By.

For example:

Step 3: You can also customise the View options by switching to the view tab.

You can customise the graph in the following ways:
displaying an area chart

connecting null values on the graph

displaying points or markers in the graph

displaying a line for threshhold value in the graph

increasing the line width in the graph

Step 4: You can also customise the Axis settings of the graph

Step 5: When you are satisifed with the customisations, click on Submit to add the Line Chart Panel to the Dashboard.