1. Make sure the extension is enabled in Safari settings:
Safari > Preferences > Extensions > enable Mate. Please note that it's Safari's Preferences, not System Preferences!
2. Check Mate's settings and make sure to enable the options you need:
3. Select text in Safari, a Mate button should appear:
4. Press the Mate button to see a translation:
If this doesn't help, please drop us an email at [email protected] describing the exact steps, so we can investigate what's wrong.