A Tor Bridge allows you to circumvent that ‘road block’ Herman, your office IT guy, put in place to stop you from accessing Tor.
When you connect to Tor, you are connecting to one of their publicly listed Nodes. From that Node, you are routed through other Nodes until you get to your happy cyber-destination. Just like Herman can block access to Facebook at work, he can block access to Tor by blacklisting its known Node IP addresses. Doing so is possible because Tor Node addresses are public (just search “tor node list” online).
A Bridge is an unlisted Tor Node. Since it is unlisted, it is less likely to be on Herman’s blacklist. Once you connect to the Bridge, you are free and clear of Herman’s road block.
The easiest way to obtain a Bridge address is to use a Gmail account to email firstname.lastname@example.org with “get bridges” in the message. You do not need anything in the email’s “subject” line. You will get an auto-reply listing three available Bridges. Of course, the easier it is for you to get a Bridge address, the easier it is for Herman to get a Bridge address to block. The idea here is more about making it inconvenient to blacklist Tor bridges than to make it impossible.
In Tails, to use a Bridge, choose Yes at the More Options screen when you log in. Then, under Network Configuration, select “This computer’s internet connection is censored, filtered…” and Login. Once in Tails, when you try to go online you will see a Tor Network Settings window; click Configure. Click No to the first few questions until you get to “Does your Internet Service Provider (ISP) block or otherwise censor connections to the Tor Network?” Click Yes and Finish. Now, enter your Bridge address(es), click Finish and it will connect to Tor.