As you enter each section of the Black Chamber, you typically encounter a new code. Each page will contain an explanation of how the code works, some history that puts the code in context, and an interactive tool that will allow you to encrypt and decrypt messages.
The interactive tools allow you to type in a message and you can often encrypt it letter by letter or with a single mouse click. You can print the encrypted message or you can cut and paste it into an email and send it to a friend, who can decode the message by visiting the website. You could even text the coded message via your phone.
In order to decode the message, your friend will usually need the 'key' that you used to encrypt the message, which is typically a list of letters or a secret word, but all of this is explained on the relevant page for that code. You will also discover hints, tips and tools that will help you crack intercepted messages.