Have a look at these:
http://jevois.org/tutorials/UserArduinoIDE.html to learn about how to connect to JeVois using a serial terminal
once you are connected, you can send commands to JeVois:
http://jevois.org/doc/UserCli.html (there are more instructions on how to connect from PC, Mac, Linux on that page too)
To turn on serial messages, you just need to instruct JeVois where to send them:
setpar serout Hard
will send to the 4-pin port, and
setpar serout USB
will send to the serial-over-USB connection. You can also use setpar serout All to send to both.
Finally, you can select the verbosity of the messages, using parameter serstyle, see here:
http://jevois.org/doc/UserSerialStyle.html
Fo that last one to work, you need to flash the latest microSD from http://jevois.org/start
Also have a look at this tutorial, where we go over setting parameters in more details:
http://jevois.org/tutorials/UserParameters.html