The RTC will allow a Raspberry Pi to know the time, even when not connected to the Internet. As such it is not essential to this project if your Raspberry Pi is going to have an Internet connection.
The diagrams show GND connections in blue, +5V in red and +3.3V in purple.
The I2C bus connections use orange wire for SDA and yellow for SCA.
You may also like to look at separate tutorials for the RTC http://learn.adafruit.com/adding-a-real-time-clock-to-raspberry-pi and temperature sensor http://learn.adafruit.com/adafruits-raspberry-pi-lesson-11-ds18b20-temperature-sensing
When everything is assembled, you can connect the ribbon cable to the GPIO connector. Remember to have the red or white band of the ribbon cable towards the SD card on the Raspberry Pi.