Team Velocity Chart answers the following questions:
What is the productivity trend for a particular team?
How does a team deliver on its sprint commitment?
To what extent sprint’s scope is subject to change?
Use it as one of gadgets on your Jira Dashboard.
Getting started
Track velocity of a single team article gives the essential information on how to configure and read Team Velocity Chart.
Refer How to install the app and gadgets article if you don’t know how to add “Team Velocity Chart” gadget to your Jira Dashboard.
Best practices
Setting up your Team Velocity Chart
https://brokenbuild.atlassian.net/wiki/spaces/~503243278/pages/3130753025/Chart+configuration#Team-Velocity-Chart-configuration explains the chart configuration, particularly each setting.