The DS18B20 is a digital sensor.
It uses a single wire to communicate with the Arduino. The communication is with a digital pin.
The protocol that is used is called "One-Wire".
So you have to use a library for that "One-Wire", and also a library for the DS18B20.
You can find a tutorial here : DS18B20 Digital temperature sensor + extras : ID 374 : $3.95 : Adafruit Industries, Unique & fun DIY electronics and kits