Trendline on chart

Hi All,

I would like to know how to draw trendline on the chart to analyze any scrip.

Pls let me know any good article or links for the same.

In Zerodha Pi , it is very easy to draw trend line on charts,  there is floating bar which is available on Pi Charts and it has all the chart tools, By just selecting the trend line from the tools and can draw on the charts, as shown below screenshot


Is there any way that I can save the trend line or drawing in pi?