Click Try it free to begin a new trial or Buy now to purchase a license.You will be prompted to log into MyAtlassian.
Click Generate license when in MyAtlassian.
You will see a screen with your license key. Here you can download the add-on. Install add-on and Apply your license sections give you prompts about how to proceed.
When all set, go to Get Started to learn how to begin to use the app.