Line charts are used to track changes over time. They are used over column charts when there are multiple groups you want to spot trends for or tracking small changes over time. An area chart is similar to a line chart, except the area under the line is shaded in.
Graphs comparing line charts and area charts
Area charts are very similar to line charts. They both show quantitative data with a time period on the x-axis. A stacked area chart is used to compare each category of the data against the whole. For instance in Nov there was just over 2 MM in sales for 2015 and 2016. We can see that Nov 2015 and Nov 2016 contributed roughly 50% each to the total. Where in this case the total is year 2015 + year 2016. Hovering over the graph lets you compare month over month.