Hi I am freshly started into Arduino projects. My first involves a GPS. I am using Parallax PMB 648 antenna. Do I use the TTL or RS 232 RX/TX pins on the unit?
so you will need to either use an Arduino model with more than one serial port
This is true only if you want to use the hardware serial port to talk to a PC. If it's a self-contained unit, you can use pins 0 and 1 and the hardware serial instance.
I agree with Richard that it is probably TTL and will go a step further and say it is nearly certain. If you needed 232, you would know it.
I have a couple of units that use TX0/RX0 and the caveat is that you have to break the connection to the device (jumpers or remove a chip/wire) when you connect to the PC to program the flash.