If you want to visit .onion sites and if you've been blocked by your ISP so you can't visit certain sites then try the Tor Browser. It uses Mozilla Firefox's code and once you start Tor Browser you will be automatically connected to the Tor Network . Once the browser is up you can use any sites you wish that where blocked by your Internet Service Provider. (Use at your own risk).
Download:
https://www.torproject.org/download/download-easy.html.en
Download:
https://www.torproject.org/download/download-easy.html.en