The PIC can't handle -10 and +10 Volt, so you can't use the RS232 port of your computer without a interface.
A PIC can only handle Voltages of 0 and 5 Volt with a very low current.
The MAX232 is a IC wat will make -10 and +10 Volt the right signal you need for the PIC, we call this a RS232 to TTL-modul.
If you gone use USB to TTL modul, you can connect the modul 1 on1 to the PIC.

http://www.electronics.gompy.net/CDI/Schema-RS232-1.jpg