DVCC/DVSS is the supply for the MSP processor core. However, digital operation introduces some ripple on the supply lines. To allow the analog part running without being influenced by this ripple, some MSPs have a separate analog supply. The voltage on them is the same (must not differ more than 0.2V from the digital one) but should be filtered (e.g. R/C combo between DVCC and AVCC to filter the ripple, separate routing of AVSS to the supply, to avoid GND ripple influence).
If there are multiple pins (xVCC1/xVCC2), all should be connected. Especially for the digital supply, as they distribute the source for the digital I/O ports, where higher currents may occur. Blocking/storage capacitors should be on each one. 4,7µF min.
And don't use them to route the supply through the chip to other peripherals (as a bridge connection).