They're on your profile.
Click on your avatar in the top right of the site, go to 'profile' and then you should see an 'Achievements' tab.
Here you'll see the achievements you've gained. If you're missing any achievements, send cstanton a message or report a problem in Feedback and Support and they'll fix this for you.
You will also see your current site rank, and your points.
If you click on your points:
You will see a breakdown of what you've done to achieve your points
