Hi,
You'd need to invert and level shift them.
I'd recommend using something like this. (Many many alternatives available of course but make sure it's designed to work at 3.3V).

I'd like to clarify that the dongle I used isn't a "USB to RS232" one but a "USB to UART", this one to be precise.

/Henrik.

EDIT: Oops, pedja089 posted while I was typing and getting distracted with other things....