I'll suggest you the pySerial Python library to read data from serial ports. You can find a very detailed explanation about the pySerial library here: Welcome to pySerial’s documentation — pySerial 2.7 documentation. Also, I'd suggest you to check this other thread: How do we use the host USB port ?, you might find it useful.
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In addition, generally it depends on what is your device you're trying to communicate with, pySerial may be a good start, but there also may be a better suited solution depending on your needs and setup.
And the full size USB port is activated by the small mechanical switch between it and the nearby microUSB port. Flip the switch closer to the port you want to activate.