To get started, you can look at the examples that ship with CVI. In particular, you can start by doing a loopback test which is described in commcallback.prj; you can also look at serial.prj. You can find these by launching CVI and clicking Help -> NI Example Finder; then navigate the folder tree to Hardware Input and Output -> Serial.
Thank you,
Regards,
JLS
Applications Engineer
National Instruments