Burndown charts are a metric that most agile teams use, especially teams that run sprints. There are various burn down charts like sprint burndown, epic burndown, release burndown etc.
Let's take an example of a team that runs a sprint for 10 days where they need to complete 20 tasks within 10 days. A burndown chart will be take to tell you if your team would be able to complete those 20 tasks within 10 days or not during the sprint. It will consistently monitor the progress of the team during the sprint.
Some of the common purposes that a burn chat helps is for
a) team members to identify if they would be able to successfully deliver their tasks within the sprint time
b) Serve as a guideline to stick to so that the team delivers on time
Tip: Never add more tasks once you start you team's sprint, this is in order to stick to the timelines. A Burndown charts also helps you understand if you are deviating from the sprint goal by adding or reducing tasks from a sprint.
Step 1 :
Go to Sprint module > and select "insights"
In the burndown chart the grey line shows the ideal line, it does a basic calculation based on how many tasks are to be completed divided by the number of days that are there in the sprint, in this case, 20 tasks are to completed in 10 days, which means two tasks in a day are to be finished. The ideal line on Freshrelease is plotted based on this calculation assuming you complete two days in a day.
Now the blue line that you see is the actual progress line when compared to the ideal grey line that is present as well. Although, its highly ideal, most team should try and stick as close to the grey line as possible in order to deliver on time. It also shows the ideal number of tasks to be completed against the actual ones.
Note: A flat line in the ideal grey line is because two days might be a weekend and no progress is expected then
Step 4: you can view you charts based on remaining tasks, remaining story points or remaining efforts
Here is an additional video link, if you want to understand sprint burndown better