The FirstClass software runs on Macintosh and Windows and is installed on all corresponding computers on Campus. You will find the program in a Folder called FirstClass Client (for Window is FirstClass). After you open the folder you can start a session by double-clicking on the FirstClass icon in the new window. The login window will appear and you can log in by entering your user id and password that you were given in class (Hit return/enter only after you entered both, user id and password).
Once you have opened a conference by double clicking on the icon, you can post a message with help of the Compose... (for Windows it is the New Message) command under the Message menu of the menu bar on top of the screen. Enter a subject title and type the message in the bottom half of the window. The default address is the corresponding conference. You can send the message by just closing the window and clicking on Send Now.
The menu bar on the top should guide you in how to reply to a message and perform other commands.
Please feel free to explore the system. If you are familiar with a Macintosh or Windows you will find that many of the features you already know will apply here.