If you want to talk to devices which are directly connected to a serial port (e.g. cisco routers, microcontrollers, etc.), select File Menu→Quick Connection. In the quick connect dialog then select Serial/Direct as the connection type. 

In the Connect to field enter the text localhost or the text serial. Then click the Configure button for Serial/Direct, check Override session profile and choose a com port via the Scan button and set the serial parameters. 

Alternately you can type the actual name of a com port in the Connect to field. In this case, the value will override the port which is specified by the Configure button. 

Important: Do not leave the Connect to field empty. You need to provide the text localhost or the text serial or the name of a serial port there.  

You can also use the host directory for these type of connections. Go to File Menu→Host Directory, click New. 

Enter a name for the entry and select Serial/Direct from the list of connection types. The Connect to field and Configure button are used in the same way as with the Quick Connect dialog (see above).

Important: Do not leave the Connect to field empty. You need to provide the text localhost or the text serial or the name of a serial port there. 

To have ZOC learn and remember your login procedure for later automatic login (assuming the attached device requires a login), enable Record keystrokes on next login in the Login tab.  

The Serial/Direct connection type is similar to Serial/Modem in many respects. However, the main difference is that a 'connection' with Serial/Direct refers to the connection between the computer and a local piece of equipment (e.g. a router), which is directly attached to a local serial port or serial usb-port.
Serial/Modem however defines 'connection' as the connection between the computer and a remote location, where the attached equipment (usually a modem) is merely a way to establish the desired connection. .  

In other words, use Serial/Direct if you want to talk to the locally attached device (router, microcontroller, etc.) itself. Use Serial/Modem if the attached device is a modem which understands AT commands and which you want to use to connect to a remote computer.  

More about the Serial/Direct and Serial/Modem connection types can be found in Serial/Direct