https://www.torproject.org/docs/tor-doc-osx.html.en
Step Two: Configure your applications to use Tor
After installing, you need to configure your applications to use them. The first step is to set up web browsing.
You should use Tor with Firefox and Torbutton, for best safety. Torbutton was installed for you. Click on the red "Tor Disabled" toggle button to turn Tor on, and you're all set:
Step Three: Make sure it's working
Next, you should try using your browser with Tor and make sure that your IP address is being anonymized. Click on the Tor detector and see whether it thinks you're using Tor or not. (If that site is down, see this FAQ entry for more suggestions on how to test your Tor.)
If you have a personal firewall that limits your computer's ability to connect to itself, be sure to allow connections from your local applications to local port 8118 and port 9050. If your firewall blocks outgoing connections, punch a hole so it can connect to at least TCP ports 80 and 443, and then see this FAQ entry.
If it's still not working, look at this FAQ entry for hints.
Once it's working, learn more about what Tor does and does not offer.