Enable the feature in "Admin home > Community"
You can also define some images for the badge, as a new tracker field in the Badges Tracker.
And then yuo can use plugin List to show that image wherever you need in your site. See the example at the documentation page for Badges:
You can also change the reward type from using "badges", as shown above, to using "credits", which reuses the feature "Tiki User Credits", which allows you to define your own points and credit system in your own tiki site.