I have a requirement where I have to show total orders per month. Now have 3 categories and have to show the 3 trend lines along with total orders as well. How I can do this?

To do that first create the line chart for a month vs quantity

Now drag categories to the color shelf which will make individual trends-

Finally, to show the total quantity, add a reference line by right-clicking on the axis and then add reference per pane.