Bridges are non-public relays. Go to https://bridges.torproject.org and solve the captcha. You'll be given 2 <ip address>:<port> combos. Go to onion icon -> Settings -> Network. Click "My ISP blocks connections to the Tor network". This has the effect of putting UseBridges 1 in your torrc config file. Then copy the first <ip address>:<port> (without the word "bridge") into the field below Add Bridge. Click the plus sign and it will be added to the list. Copy the second <ip address>:<port> into the field and click plus again. Congrats, you're using bridges.