"Conn" stands for CONNECT. Selecting this will cause your station to connect to the call sign listed under "Options".
"Disc" stands for DISCONNECT. Selecting this will cause your station to be disconnected from the remote player.
We assume that you have setup your Mac to talk to your TNC at 8 bits, no parity and 1 stop bit. The baud rate is up to you and can be set on the options card.