You need to look at the sensor's manual to determine if it uses the RS-232 protocol, or whether they mean something else by "serial". Serial can also mean something like SPI. Assuming it uses the RS-232 protocol then you need to see what it says in the manual regarding the hardware connection - i.e., what kind of cable. Then you need to see what it says in the manual (see a pattern here?) about the protocol's parameters (baud rate, number of bits, etc). Then you can use HyperTerminal (if you're on Windows - use something else on other oeprating systems) to try to communicate and get data. Use the sensor's manual to see how you're supposed to communicate with it. Then you can move up to try the serial port examples that ship with LabVIEW.
You may also want to review the following: Serial Instrument Control Tutorial.
To learn more about LabVIEW it is recommended that you go through the tutorial(s) and look over the material in the NI Developer Zone's Learning Center which provides links to other materials and other tutorials. You can also take the online courses for free.
