Hi,
In the order that they appear in your question, and with reference to the datasheet, the voltage (?) symbols mean:
V1 - Not in datasheet
V2 - Not in datasheet
Vcc - Not in datasheet. However Vs is in datasheet, and means Supply voltage
VEX - Not in datasheet
VOUT - The output voltage from the sensor
The Pin numbers for the small outline package and for the unibody package are given at the bottom of page 1. You need to cross-reference these to the pin numbers as they appear in the package outline drawings on pages 7 to 9.
Decoupling capacitors are to shortcircuit (or in more formal language: to offer a low impedance to) high frequency voltage spikes in the power supply (between Vcc and ground), as well as in the output voltage. If not decoupled, such spikes would produce erroneous results from the sensor. Such spikes are more commonly called noise; such erroneous results are more commonly called glitches.