When you're setting up a connection with somebody and trying to find settings which yield reliable transmission with the best fidelity, it's nice to have a back-up form of communication which will work on all but the most unreliable Internet connections. Speak Freely's Text Chat feature provides such a back channel. Use the Options/Text Chat menu item to display the Text Chat window, which you can position wherever you like on the screen. To send a line of text to everybody you're connected to, simply enter the text in the Input field and type Enter or press the Send button. The text will move up into the scrolling transcript area, prefixed by an arrow identifying you as the sender. When received by the people you're connected to, your message will appear in their transcript area prefixed with your name (or E-mail address, or host name, or IP address in descending order of preference based on the information you've entered in your directory entry). If the text chat window isn't already open at the receiving site, it will pop up automatically.
Speak Freely text chat is not intended to be a full-functioned chat client; just an aid in setting up voice connections. It's easy to think of lots of features one might add to it, but all of these and more are available, and have been for years, in purpose-built clients for protocols such as talk and IRC. If you're primarily interested in text chat, it's better to use a program specifically designed for that application, not Speak Freely.
Note further that Speak Freely text chat messages, unlike audio communications, are not encrypted even if you've enabled one or more forms of encryption. Don't send any sensitive information over text chat; wait until you've established a solid audio link and use voice instead.