Click Help>>Find Examples to open the example finder.
In the tree, open Hardware Input and Output>>Serial and you'll find several examples of how to use the serial functions. An important thing to understand is that recent versions of LV use something called VISA to communicate with the serial port, so you will need to have VISA installed. Also, the port name may not appear as COM1 but as something else (ASRL::INSTR1).
For futher data, search this site for VISA or serial.
Also, I suggest you read the LV manual and that you try searching this site and google for LabVIEW tutorials.
Here is one you can start with. You can also contact your local NI office and join one of their courses.
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